> Nature is not morally right. In fact, nature is amoral. Pointing to nature and saying "nature does it so it's ok" is a bit like pointing at a landslide and saying "nature does it so it's ok to build my house like this". It's meaningless.

Completely agree here, luckily I never made that argument:) I basically made a tongue in check throw away remark

> Killing any kind of sentient creature whose death could have been avoided is immoral (whether legal or not)

Here we disagree if by sentient creature you included animals, which I'm assuming you do or you'd just say humans:)

Look I recognize your name on this site now and I respect a lot of what you say but you just can't make this statement and assume its a fact that isn't debatable. Because its very much debatable.

Look we just disagree on this point, which is fine as its all opinion based and no right or wrong here.

Everything's debatable! But there are pretty strong arguments for "killing sentient beings is wrong".

Most morality stems from the Golden Rule (treat others as you'd want to be treated). If we take that as a given (a reasonable non-controversial starting point imho), then we can easily agree that breeding and killing other humans for food is immoral.

The Golden Rule is generally applied to a small subset of sentient beings, of course. However, one thing is observable throughout history, which is that the group of beings included in the Golden Rule has generally gone up with time. It used to be only a subset of humans, and has progressively grown to include most (and yet still not all) humans in most (still not all) cases. But it continues to grow. And already some types of treatment are considered abhorrent even when applied to non-humans.

For example, we may debate eating pigs, but we would presumably all agree that deliberately torturing a pig for your own personal satisfaction is immoral (hence all the laws against cruelty to animals).

This progress of history seems pretty constant - it may be the only progress we can measure as far as the question "are we getting more civilised" goes. Our measure of progress is, how many more groups do we include under the shield of this Golden Rule.

It's pretty reasonable to predict that, unless things go very badly for humanity, eventually many animals that we currently breed and kill for food will come join us on the safe side of the Golden Rule. We may start with the more inspiring or cuddly ones like Dolphins or Whales, but can you doubt that humanity from 500 years in the future will consider eating a dolphin as abhorrent as we would consider, say, eating someone's pet labrador?

Did eating someone's pet become less moral over time, or has it always been immoral, but before it was tolerated? What about eating other humans? What about other applications of the Golden Rule?

Obviously you can respond that morality is a moving target... and you're right. But then you're still agreeing that the topic we're discussing is something that could easily be conceived as immoral in the future (unlike, say, petting a cat or painting a nice painting, which are unlikely to ever be considered immoral as far as we can predict without resorting to extreme scenarios).

I take the view that something which will be immoral in 500 years is already immoral, we're just too undeveloped to realise it yet, much in the same way that I'd say that death penalty or torture were always immoral, but people weren't civilised enough to realise it in the past.

> It's pretty reasonable to predict that, unless things go very badly for humanity, eventually many animals that we currently breed and kill for food will come join us on the safe side of the Golden Rule. We may start with the more inspiring or cuddly ones like Dolphins or Whales, but can you doubt that humanity from 500 years in the future will consider eating a dolphin as abhorrent as we would consider, say, eating someone's pet labrador?

Interestingly, humans rarely live as a solo species. Most concentrations of humans are part of a larger menagerie of symbiotic utility and pest animals that rely on human existence and activity and despite the constant presence, it's rare that those animals ever enter even the most carnivorous human diet outside of very specific cases.

But it's not, meat is so essential to human diets that unlike all other non-meat eating animals, we evolved away the mechanisms for surviving on plant only diets (or at least the kinds of plants a human would be expected to find in their local environment - shipping scientifically engineered and manufactured yeast paste halfway around the planet is kind of cheating).

Reducing the arguments to "because we don't strictly need to, modern civilization can construct a balanced diet without meat" requires that we follow this argument and consider all elements of chosen behavior that go beyond what modern society has made possible that will strictly allow for life-sustainment and reduce life to an ascetic, needs only, life-style where every person is "morally" wrong for occupying more than a 6'x8' housing unit that are stacked into constructs as tall as modern engineering will allow and for using more than x number of joules for life-sustainment etc. etc. ad nauseam. Arguing that doing anything other than strictly necessary life-sustaining activities is morally questionable becomes absurd.

Is meat that essential to human diets when millions upon millions of non-meat eaters have successfully lived without consuming meat?

You simply can't say that meat is "so essential" because it clearly isn't, any more.

I eat meat for no other reason than pleasure, convenience and laziness but I, and most probably everyone else on the planet, could easily sustain a healthy, long life not eating meat.

Yes. There are specific nutrients that humans can't synthesize and have absolutely zero plant sources. The obvious one is animal protein, which is structured and metabolized differently than plant protein. But more specifically:

- Vitamin B12, you don't need a lot of it (a few grams of meat per week provides more than 100% of the dietary sources), but every single study of populations of Vegans shows that the majority of them are deficient and have Hyperhomocysteinemia as a result. Hyperhomocysteinemia is only ever seen in four populations, the extreme elderly (due to age related nutrition absorption and metabolic issues), third world countries with chronic poverty, extreme alcoholics and vegans. You can get by for a very long time as B12 deficient, but it will catch up to you and the result isn't particularly pleasant. https://news.ycombinator.com/item?id=6883090 some more I've compiled on this

- DHA (Docosahexaenoic Acid), an Omega-3, pretty much available only from animal sources (and a very small algae source which is often used as a supplement precursor) has been shown important to normal cognitive functioning. Every study I'm aware of has shown that vegans are deficient in DHA (even though it can be synthesized from ALA which is the kind of Omega-3 found in flax seeds and chia etc. it's preferentially synthesized to EPA another Omega-3 which also has plant sources). Omega-3 is essential and not all O3FAs are equal. Despite being able to find DHA in algae in sea vegetables, most vegans simply don't eat enough of it.

- Vitamin A - readily discussed in Vegan sources as "available in plants, but hard to get sufficient quantities of a complete source". Vitamin A is a group of compounds, not just one, and plant sources don't offer a complete source. It's readily available in animal sources, especially liver. Vegans are typically deficient in retinol which is used in the development of epithelial cells an essential and basic component of animal tissue.

Non-essential, but had to very hard to impossible to get in plant form in sufficient quantities (i.e. studies of vegan populations show shortfalls in the majority of the studied population):

- Arginine (partially synthesized by humans, but needs to be supplemented by food sources. Animal sources are much better sources than plans. But if you eat sufficient plant sources, which majority populations of vegans have been shown not to do, you can get by.

- Creatine, synthesized by Arginine, along with Methionine (which is better sourced from eggs then plants as well) and glycine (which is readily synthesized by humans), has been shown to be majority population deficient in every study of vegans I'm aware of. Creatine is important for muscle development and maintenance. You'll find that vegan athletes are aware of this dietary shortfall and supplement.

- Carnosine, only available in animal sources. Carnosine has been shown to be an important dipeptide and important in normal muscle function (where it can be used to significantly boost performance with sources of beta-Alanine). It also has been shown to be a major preventative factor in Alzheimers, Diabetes proper skin function and various age related illnesses suggesting long term consumption is important for healthy long-term living.

- Vitamin-D - especially in northern latitudes or people who don't get enough sun exposure. The primary dietary sources are all animal sources (beef liver, eggs, cheese, fish, etc.). Vegans have shown to have higher rates of vitamin D deficiency than other populations.

and it goes on and on and on.

Vegan diets also make adequate nutrition decisions and monitoring more complicated. For example, complete Zinc intake should be at around 15mg per day, but diets high in phytates require more as phytates disrupt zinc absorption. Similarly iron intake has to be measured at higher doses as what humans actually need is Heme, which is synthesized from Iron. Heme only has animal sources, which is generally used to explain anemia that's common vegan populations.

In addition, animal sources are simply required for normal child development even if adults can get by for longer periods without some of the above. Studies of children raised on vegan diets show significant health and cognitive deficits as animal sources are either the only or the best sources of critical bone, blood, muscle and brain development.

Long term studies of vegans have shown that over 90% of vegans are deficient in one or more of the above, despite supplements being a traditional part of the vegan diet. Most vegans do not stay vegans for more than a few years as the health and nutrition deficits build up, they'll wax on and off the diet -- this provides essential B12 at interval, and since B12 doesn't require constant intake, is usually enough to keep off the worst effects of B12 deficiency. Carnosine however has been shown to be a significant problem in long-term vegan (and vegetarian) diets and is generally attributed to the reason why vegans, despite being healthier in several categories, die at ages and rates similar to omnivores.

Every single one of these deficiencies and health issues are solved on normal omnivorous diets.