Some religious groups are more of a threat than others, based purely on past history, and currently stated aims of some fundamental groups. We can argue how useful past statistics are in predicting future behaviour, but the point still stands.
This is fact - some people are scared of facts that don't strike them as PC, but it doesn't make them any less true.
It is also all relative, and there are factors other than religion that greatly outweigh it in terms of added risk (a history of odd trips to Pakistan, for example). The added risk over another religious group, across the population at large, is without doubt so tiny as to be completely irrelevant to the travelling public.
Some airlines refuse to seat men next to unaccompanied minors, because there is a greater chance that they are sex offenders. The chance is still absurdly tiny, but it seems that the PC crowd don't get up in arms about it because it isn't a currently fashionable thing to moan about, like race and religion are.