Never smoked anything in my life, having one side of the family wiped out prematurely by nicotine, all of them.
Lived in Colorado. The pros outweigh the cons a million to one. The biggest positive was the massive reduction in DUIs, since people drink in bars but smoke weed at home. There may be a reduction in harder drugs, too, given how much easier and cheaper it is to get weed. The tax revenue from weed sales is huge (was bigger, though) and because the laws were changed after Colorado turned liberal-ish, the money was mostly allocated to great causes.
Government loves having a law that can be selectively enforced and is broken by a lot of people. Taking it away is a huge plus, especially in times where the government is looking for easy ways to control the population. Even before now, White people caught in possession or smoking marijuana rarely got more than probation, while some Black people were three-striked for the same.
The only downside is that it still smells bad, and I am still not sure that hacking up your lungs is all that sane or safe.
Yes, it appears that young humans can have very negative reactions to weed, and that it can affect their brains negatively. That would absolutely be a problem if legalization increased week use among teenagers, but that doesn't seem to be the case.