Guilt resolves nothing. The issue regarding slavery is one of understanding, not guilt.
I am neither for nor against them building the Park 51 mosque, but calling it the 9/11 mosque is just stupid bigotry. The owners of Park 51 have the same right to build whatever they wish, just as you would if you were the owner.
I do not see where any sane person can say that a place two blocks down and one around the corner is "sacred". I do not see how victims who were simply doing their jobs and unlucky enough to get murdered by fanatical morons make any place "sacred".