I do not think that faith in and of itself is a negative thing, I see it more as a motivating factor; but I do think that faith without reason can be an unskillful motivating factor when it comes to our actions, i.e., acts leading to harmful results. People who kill thousands of other innocent people out of faith is certainly one example of how I think faith can be an unskillful motivating factor.
Nevertheless, is faith, as opposed to skepticism, always going to lead to such behavior? On the issue of faith in Buddhism, for example, while there is certainly room for skepticism toward matters of faith, there is also a limit to that skepticism. The Buddha often stated that faith in a teacher is what leads one to learn from that teacher, to put their teachings to the test to see what results they will bring; and the only valid basis for faith is the instruction that, when followed, brings about the end of one’s own mental defilements (DN 11).