The vast majority of my friends/acquaintances use alcohol. The vast majority are sane, productive, rational. I do know a couple of what I consider to be functioning alcoholics.
A plurality of my former (liberal) friends used marijuana. A majority of them went on to harder drugs, had mild to serious mental issues, and were less and less productive until they became just about inert. Except for the few that quit.
I wouldn't claim any drug is benign or completely harmful. People are benign or harmful. That being said, the majority of people I know that imbibe in hard alcohol have major problems, while the majority of pot users I know are responsible productive citizens. So I guess my anecdotal evidence cancels out yours.
And, I have no doubt a lot of them and smoke pot with them. Isn't that the reason you want to legalize marijuana?
Anyone with brain should realize we have enough legal ways to get intoxicated and don't need to lose any more lives by legalizing new ways for citizens to become high. Marijuana legalization diminishes the quality of life for all and that is why it has been disaster in nations and states that have done so.