It is well documented that marijuana can cause psychosis in some people that are predisposed for it. I know quite a few people, my self included, that started using cannabis way more often after it was legalized.

I think it's reasonable too assume that legalization of a formerly forbidden substance will increase overall use of that substance. I also think that it is reasonable to assume that increased use of a substance will increase the amount of people suffering the potential side effects.

That said, I think social media, the economy, the pandemic, pollution, and the war on terror drugs have done way more harm than legalized weed.