It's simple, if the situation proceeds to be as it is in the middle east, or worse, millions of potential visitors won't feel safe to go to Qatar, no matter how much the Qatari will try to convince them that it's safe. And rightfully so. If I know that some 70-80 km from Qatar people are being shot in Bahrain and there are serious demonstrations, I won't feel safe in Qatar.
If there was a world cup during world war II, noone in his right mind would have organized it in the neutral Switzerland. It was gonna happen in South America or something.
If the situation won't be completely calm after 5 years, then FIFA should give that WC to someone else, far from the middle east.