Today, most people are "more vegan" than meat eater, too, as in they eat more grains and vegetables than meat. If that's what you meant.

There's no evidence to support that. Best evidence is that our ancestors for the longest time were likely opportunistic omnivores. Plants of course were a large part of the diet, but looking back to about 3.9 mya meat was on the menu.

https://en.wikipedia.org/wiki/Australopithecus_afarensis

This study was funded in part via an unrestricted research grant from the Beef Checkoff, through the National Cattlemen's Beef Association.

I think people on the left as whole would be more prone to depression and anxiety too. People who care about the world are generally more concious, more self-aware and critical, which turn into more worrying and at the extreme, anxiety.

I mean, the part you cited already mentioned it but later in the study it's stated even more clearly:

Across all studies, there was no evidence to support a causal relation between the consumption or avoidance of meat and any psychological outcomes.

vegan diet is literally making people crazy

Wrong.

(or crazy people are more often on vegan diet, dealer’s choice).

Mmm, no, there is a right answer and it's this one. Well, it's this one with more inclusive language. Like "People who have experienced more hardship with psychological consequences are more likely to avoid consumption of animal products".