Of course the reason that people don't care enough to change their lifestyles is because

> A healthful vegetarian diet is not hard to achieve, at least no harder than a healthful non-vegetarian diet.

Might be true but isn't sufficient

It's still way easier to have an omnivore diet than a strictly vegetarian one. Partly that's due to how society is currently structured, but people still ate meat long before society was structured this way. Because it was easier.