Bill O'Reilly appeared on The View this morning, and when the conservative pundit blamed 9/11 on Muslims, tempers escalated ... with Joy Behar and Whoopi Goldberg walking off the set.

The drama started after O'Reilly said, "The mosque down here on 9/11. That's inappropriate."

Before storming off, Goldberg responded, "You're saying that Americans are not smart enough to recognize that while it is part of our Constitution to say freedom of religion and freedom to worship and there were 70 families who are Muslim who also died in that building. So you're saying that his saying that they have the right to do it and not saying anymore is why his approval ratings have gone down?"

O'Reilly then added, "Muslims killed us on 9/11."

Barbara Walters immediately criticized her colleagues for walking off, insinuating that it was unprofessional.