Come on, everyone is different and plenty of people (the majority?) can use them responsibly. And drugs are vastly different as well so classifying them as as such seems fairly counter productive to any discussion.
I'm probably the nicest person that you could be around when I'm high or drunk. I don't get into fights or do anything to harm others (accidental self-harm on the other hand...). I've never managed to destroy a relationship due to my substance use.
I've never woken up in the morning and had to worry if I've left a trail of destruction behind me. Sure I've done dumb shit, but it's never hurt anyone else.
I'm actually more of an arsehole while I'm sober. I'm a nicer and more agreeable person when high, which is its own problem that I've been working through.
Drugs bring out our most base traits. For some that's a good thing, for others it's not.
Drugs are the demon that I thought I'm good enough to control -- I have a fucking Ph.D. after all. I know the answer for myself now, that is doing marijuana or any other drug is a losing battle. Most of the times when I am sober, I can hide the asshole person I really am. But when I'm high, all hell breaks loose.