Whatever facility we may enjoy on their turf can always fruitfully be utilized. My personal experience is that trolling on Muslims fora has stopped. all thanks are due to Allah (SWT) for that. This has resulted in a sort of lull on our fora. Thus any body having any spare time at his disposal can use it for Dawah. If you are polite enough you should get a chance to say what you want. At the most they might ban you after some time but frankly I do not envisage that possibility. They do make their own decisions and they shall do that in case of choosing Islam. And it is their right. The thing that is at stake is our duty - we are not doing that. We only have to learn to wiggle out of certain sensitive situations otherwise the rest of the sailing should be smooth - if you can manage to ignore the initial insults. And Allah (SWT) knows the best.