Ive posted my argument as many times as ive needed to respond to yours! Without knowledge of the statistics, who are you to say whether or not self control without intervention is enough?
I was not at the asifa in fact, so another horrible guess. Smoking is allowed in yeshivas because it aint as cut and dry as you claim it to be. They dont allow bochurim who are addicted to treif food to eat treif food, irrespective of their addiction to it. Smoking is allowed because bochurim are not in prison, they have the right to make and rectify their own mistakes, so long as they are not infringing on halacha. Before you jump down my throat about how assur smoking actually is, i wont entertain that argument, its been done by many greater people than myself and yet is still inconclusive.
oh, and smoking may not be banned in yeshivas but in my limited experience, pornographic material or anything which even smells remotely similar to it is completely unaccepted.