Tim Fernholz writing at TAP gets to the heart of the manners question:
The debate demonstrates how the project's critics simply assume that it is offensive for Muslims to celebrate their faith two blocks from the World Trade Center, to the point where they simply take the proposition as self-evident. Cupp kept repeating the phrase "common sense and decency," as if those terms are defined a priori, but couldn't explain why it's common sense that Muslims worshipping near the World Trade Center is indecent. That's because it's not common sense -- unless you happen to blame the religion of Islam for what happened on 9/11. It's an ugly kind of bigotry to admit.It's offensive to even entertain the manners question.