It is a drug, but no more harmfull or addictive than many other legal drugs, like caffeine,
But lets not kid ourselves, marijuana is the shit!!!
I wouldnt say it has ruined my life, but it has definitely made some aspects of life... monotonous, It is also addictive, anyone who thinks otherwise needs to do some research on addictions, how they work, what causes them and what they are. And like all addictions, it will probably partialy lead to your death if you smoke it all the time

but fear not no more than your addictions to certain emotions.
But I digress, pot has helped me through some of the hardest times in my life, its been there when noone else was, it gave value to my life until I was ready, or able to find value elsewear.
It has given me so much time, and taken away so much more, I consumed it util it consumed me. It's made me happy when I was sad, and calm when angry, it made me interested in things I never would have been interested in had I not been high as hell! It gave me time to read, learn, sit, watch, observe, quietly from a corner, that I sat in for years. It has taken away from me though, in a psycological way, or maybe not. Still I've learned so much from pot, and have probably fogoten twice that.
Its a trade off, at least for me, not a real, or natural one, but one that I have created, weather or not I would have been able to without it is something I'll never know, it makes you think... anyway for now, I'm going to stay here and smoke me some weed!