I tell them, "Yes, and 500 million years ago, dinosaurs roamed Manhattan, but I don't live in either of those times, so I don't worry about dinosaurs or Christians trying to kill me!"
Quite.
However, this is where I break company with many of the anti-Islam crowd.
Both Judaism and Christianity have episodes in their past of extreme violence for religious reasons. Both religions have for practical purposes evolved out of this.
I see no reason Islam cannot do the same, though admittedly it will be more difficult due to the centrality of religious violence to the faith.