I think we are humans first before we are photographers. Helping others should be more important than taking a picture, if we have to choose between the two. But if help is not necessary or can't be done, I don't see any problem with taking pictures if the intention is to record the event, not to take advantage of the situation, to sensionalize, etc. (however, intent is hard to figure, it's more of a personal internal thing that only you will ever truly know, so that's for your conscience).
I remember I was walking along a street once, and a building was on fire. I was saddened by the tragedy, but I also found the firefighters' efforts to save it something I wanted to capture and wished I had my camera with me at that moment (I didn't, it wasn't a very safe part of the town, you only carry what you absolutely need when you go there). Afterwards, I wondered if I was being calloused by thinking of it as an opportunity for picture taking, but I don't think it's wrong. As long as we don't forget that we are first human beings.
Besides, a picture might help--for instance, you might be able to record people and circumstances that no one else saw, which might help, say, solve a case or something.