I would call it a mild-to-moderate self-hindrance. Not destructive per se, but not a tool. Can eventually add up to a serious waste of time and money.
My story is as follows. The high from smoking it always kinda forced me to be a kinder person for a day or 2, but it also made it harder for me to control my temperament when not smoking. It's not good to always be 1-2 days away from being very irritable.
That being said, I believe people should be free to do whatever they want with Cannabis. It is not nearly dangerous enough to warrant throwing people in jail and slandering their name with criminal charges. Legalize it.
–Signed, someone who smoked for 15 years, with a 3 year break in the middle due to legal problems.