When people who have never smoked marijuana make blanket comments about it's effects they are almost always WRONG.
People who have addictive personalities and no self control are just as likely to become addicted to hard drugs no matter if they ever smoke weed or not. Marijuana is not nearly as addictive as alcohol, and arguably not nearly as dangerous, and yet most people who condemn it's use would just as easily stop for a beer at a local bar, or have a night-cap before bed.
Also, I have played in, worked at, and frequented a LOT of bars in the midwest and the southwest, and you are much more likely to get offered coke when out at a bar than you are pot. So whats the real gateway?