Well written, and I understand your abhorrence of the group and its message, but as long as they make the venue available equally to all groups/beliefs, it's no different than the ads on buses or public benches. If you rung them up and said you wanted to put up banners that said "Don't believe in god? You are not alone" and they said no, then it would be a problem. If they said sure, just pay up like the other guys, than there is no conflict. Mind you, I don't like it or approve of it any more than you; I just don't think there's anything that can (or should) be done so long as it's a simple business transaction open to any group.