It's not that the forum is only for US citizens, but that this is an issue on which many of us frankly are not interested in what anyone who is not a citizen thinks or has to say on the subject. As a non-citizen, you are our guest. A welcome one as a legal resident alien, but a guest. Just as I would be a guest in England or elsewhere in Europe.
To me, the view on immigration of every citizen, whether I agree with it or not, has infinitely more weight than your opinion.
Read my post 1013.