if you try “leftists (or liberals) more likely to be mentally ill” in a search engine you see things like:

American adults who identify as politically liberal have long reported lower levels of happiness and psychological well-being than conservatives, a trend that mental-health experts suspect is at least partly explained by liberals’ tendency to spend more time worrying about stress-inducing topics like racial injustice, income inequality, gun violence, and climate change.

https://magazine.columbia.edu/article/why-depression-rates-are-higher-among-liberals