I agree with Mr. Davids on that abusing any drug is bad, however you mentioned with the entire gateway thing... that can be true for some. However, I believe when using any sort of substance or drug (other than alcohol/cigarettes which have been proven addictive) it really depends on the person using the substance. For example, I know of people that started smoking marijuana and eventually it kind of took over their life and eventually they'd even start to sell it and with all of this activity they'd meet new people who would introduce them to new drugs. But for another example, I know many of my friends and other people that have only used marijuana in their lives and never went to another drug... I believe it depends on the mental state of the person and how strong they are in terms of resisting to try other drugs, like myself I've only used marijuana in my life and I don't plan on going to any other drug.

Also, bang on Shane.