Applying rational thinking to beliefs is not damaging to people. I think it's important to remember that and not to confuse the two. Of course it is not allright to attack people verbally, but it is allright to attack beliefs. Otherwise human progress would stagnate. One only has to think of all the wacky beliefs people had in the past which are now widely regarded as, well, wacky, to put it mildly. There is no difference between arguing about whether the earth is the centre of the universe or not and arguing about any other issue of interest or importance to humans.
Inevitably, many people think their beliefs are bound up with who they are. This may well be the case, but they are not their beliefs. The beliefs exist separately from the person holding them. So attacking (that is arguing about the validity of) beliefs is not attacking the people holding them.
If people choose to be offended when something they believe is argued about and refuted, that is a personal problem they have. The problem is not caused by the fact that a belief is being attacked.
Attacking a belief IS NOT THE SAME as attacking a person.