As I predicted, the purpose of this post was vegan debate, and my answer has been completely ignored.
If there's a diet you'd like to discuss that involves not eating fungi then go ahead and make a post for it.
It is clear the question asked is a ruse to goad people into a vegan debate.
If you take OP as being 2 questions, then the first answer is at the beginning, and the answer to the goading question of food scarcity is the end.
But the answer is clearly not what OP was after. Only vegan preaching was intended.
EDIT: Your concern as to whether I was snarky in my response glossed over the fact that there is an answer. Let's talk about that instead of proving my "snark" as the more important yet correct part.
Look at your sibling comment for an example of a comment made by someone who actually cares about discussion and not winning stupid word wars. You both said the same thing in essence, but they don't come off as a prick.
Verbal cherry picking is annoying to all except those in the echo chamber. Nobody has ever said they eat hamburgers only because carrots are so hard to come by. Scarcity is a clever ruse, but doesn't work here.