Has that battle ever been waged in this way and been lost? Or did they pick marijuana and not fight the other battles because smoking and drinking is so entrenched in the community?
The battle against smoking and alcohol was much harder to fight because their downsides only became apparent after it was so entrenched. Rabbonim probably assume they have a better shot at winning the war against marijuana because it's not widespread now.
Color me skeptical you can find me even one person that thought marijuana was perfectly OK until he read a kol kore that opened his eyes
I did not say people who think it is perfectly OK. I said curious people. Every smoker had their first cigarette. If they are young enough, they knew it was not healthy, but they were curious enough (or under peer pressure) to try it. Kol korei's against cigarettes would not dissuade them, because it's too prevalent for people to put so much weight in kol koreis.
But a standard yeshiva bochur, who would not try a new phenomenon if he knew rabbonim all said it was assur, would generally refrain from taking that first dose of marijuana. That is my perception.