I have used cannabis recreationally a few times, and each time I feel slightly mentally impaired (slow thinking) for days afterward. It has completely scared me off from using it further.
I do know a few individuals who have smoked pot regularly for decades. I don't see cannabis having had any negative effects on them or their families. They are intelligent, successful people in long term stable relationships.
Having known a lot of older daily smokers (decades) and older alcoholics, alcohol is a lot more damaging, both mentally and physically. I've never seen anyone die in their 40s from marijuana, but I've seen a few people eventually lose that battle with their liver or their kidneys from alcohol. Older alcoholics can be almost shockingingly stupid, too - far worse than young alcoholics.