Actually it was Rabbi Kahane that opened that door. Newt is a bit of a late comer, but I'll take it anyway.
You make a valid point. However Rabbi Kahane is considered to have been an "extremist" by a lot of people. Huckabee and Gingrich are considered more mainstream, so them talking about this makes it easier for more mainstream candidates to talk about the issue.
I wish more people were "extremists" in the right direction, or to put it another way, "moderate" like Chaim.