A couple of questions: would you have shot Rodney King being beaten by LA cops if you'd known you could do it safely? Would you have made the photos if you'd known that King was no more than bruised and your photos would, after processing through the media, result in the LA riots in which millions of dollars in property was destroyed and several innocent people were killed?
As one of my least favorite presidents once commented, important questions may have simple answers, but not necessarily easy ones. Whether or not to take a photo is not necessarily an easy question.
For example, would you risk yourself, even a little, to take a picture of a Russian soldier beating or killing a Chechen, if it wouldn't make any difference to anyone one way or the other? I mean, if you could show it to the Washington Post or Newsweek and they'd believe you, but just blow it off as insignificant (as "not news")? One of the realities of some third world nations is that photography simply won't make a difference; and if it won't, should you take a risk to do it?
The answer, I guess, is "sometimes." One of the reasons the brutal effort at genocide by the Hutu against the Tutsi in Rwanda got as far as it did was for lack of the kind of documentation that would have so enraged people in certain nations (like France) that the country's politicians would have felt obliged to put a stop to it. Might even have been possible to do that kind of photo documentation, if anyone had been interested before it was too late...
Actually, now that I think about it, I don't believe you'll find a good answer to this question on a photo forum.