tell them to grow the fuck up if they're living in a sort of dreamland where they get what they want when they want. grow a pair girl. make us stoners proud and be yourself. if you truly hate them, ask to move dorms. don't make yourself miserable.
At first I'd say swap rooms and find some like minded friends. But then i think back and learning to compromise with people who you don't like in tight quarters really will help you in the long haul
You are paying just as much money for that room as those girls, so do what you want in your own space. If you want your weed poster hung up, then do it. As long as you dont have any in your room then don't worry about it. I actually had the same problem, my room mate accused me of being a big druggie and doesnt hates my trippy posters. I just told her I am going to do what i want, and i havent disrespected her in any way. Be the person you are, dont let them try and turn you into you anything different. good luck!
I'd tell them to go fuck their ignorant selves and move out. For my own good. If you don't have that option though . . . I don't know. Try reasoning with them? Appeal to their sense of fairness and democracy?