I started out thinking just like you. But I spent 25 years in the field and saw the problems first hand day after day. I like numerous emergency room doctors and nurses that I worked with found out the truth.
People who eat too much candy and fast food, use tobacco products, drink too much alcohol or use crack cocaine, meth or heroin will almost all admit that what they are doing is bad for them. It is only marijuana users who typically insist that it does not causes them or anyone else any harm. This is despite numerous studies that prove all sorts of negative effects from memory problems to severe psychological issues to unsafe driving to severe vascular problems.
If you are a heavy marijuana user I can name half a dozen problems that you are most likely suffering from but will not admit Marijuana is causing. Marijuana is a scourge to individuals, kids and young adults especially but it is also a scourge to our society. You are a fool who will continue believing what you want to until the day you die. But don't push your nonsense on others. That is not nice.
I don’t use marijuana.
Supposing your nonrandom observations extrapolate to the larger population ... what of it? Harm is harm.
Tell it to Willie Nelson.