I know how you feel... In my degree theres a lot of talk about abortion (along with embrionic stemcell research, and human cloning, but thats another story) and the majority of my classes are pro-choice. The discussion often comes up in the common room, and most of the time I just sit there and add peices of information, rather than discuss my views.
I feel sometimes that if I said what I really believe that id be attacked for it. Its not really fair, but there a choice. You can chose to say what you think and then you will find out which friends are ones that respect you. The biggest thing is to be able to support your claims with facts, figures and evidence. If you back up your views, present them in the approperate manner, and have lots of retaliation ready, then you should be good.
I came accross a similar thing today actually. I was having lunch with some new friends when the topic of having kids (now) came up. My 3 friends were all like \"no way could I look after a kid (they are between 17 and 19), I couldnt do it, I barly look after myself. I dont want kids till im 30\" Which struck me as rather interesting, as im the opposite. However, they all live at home with mum and dad, dont have there own transport (or drivers licences), nor jobs, and only one has a boyfriend. So I can kind of see where they were coming from in thinking they wernt ready to intentionally have children. Though I think they would have looked at me weirdly had I said I wanted a baby now...
Oh well.
Sorry for the ramble!