Not true. While I prefer to be an omnivore, and in a collapse you'd likely need to be one, most of the world's people are vegans because they don't have access to livestock, but would most likely prefer to be vegetarians eating the occasional egg and milk.

How can you support your claim?

It's true that certain nutrients are not as available or that the bioavailability of the nutrient like calcium is less condensed than say, milk, something I recently wrote about in my signature here, but there are other options in the bean family.

A lot of people are changing their diet to something like vegan because of interest in that lifestyle, but I agree that ultimately their health is not better they don't vary their diet and could end up with nutrional defficientcies. However you could equally say the same with a Western diet.

If you can't grow your own food, whatever it may be, then you don't have food security. And in this time of great uncertainty, potential dollar collapse, inflation, severe loss of property, etc then it only makes sense to learn skills that will allow you to do so.