I've never been hurt by being nice to someone. I've had people be rude in return, people try to hurt me when I'm trying to be nice, and often people that just don't seem to appreciate it. None of those matters to me though, because I'm not nice to get a direct positive response from others, and the only people that can hurt me, most likely won't. The closer I am to someone, the more trust I have in their judgments. For others, I don't have much trust at all and I can only be affected if it proves out to be true, but by that time, it's almost always beyond the point that it can hurt me and become academic.
Also, I don't think that fear in itself is irrational. Though many people have a lot of irrational responses to fear, I don't think it's fair to blame the responses to fear on the fear. Fear, like most other emotions is a driving force or a warning, so just feeling fear is not necessarily irrational, at most I think feeling fear is arational. If you're scared of something, there is a reason for it, not always a good reason, but there is a reason. Just because one feels an emotion, doesn't make them irrational, nor does feeling an emotion have to lead to irrational reactions.