The example of photojournalists snapping pictures when something potentially tragic is taking place is a hard one. As a human being, you think that it's either irresponsible or insensitive of him/her to be snapping photos at a time like that, but as a journalist, I guess you might feel that it's either your job to do it or even on a deeper level, the role you play in moments like that to capture a news event or little bit of history.
An example of one recent photo I passed on snapping - I was on the sideline at a high school football game taking photos of the game when a running back I had just photographed being tackled came off the field right in front of me. His arm was obviously broken just above the wrist jutting out at a right angle to the rest of the forearm. His coach and the trainer grabbed him and held him so that he couldn't see the damage as he started to cry out, in more disappointment that his season had ended than in pain, at that moment.
They were right in front of me and a photo would have captured everything in perfect detail if I had snapped it, but I just couldn't. I did consider it for a minute; after all, I was there to report on the game, this was their #1 running back and it was near the end of a season where they were in contention for post-season play, but their chances had probably ended at that moment. It was sports news, but I just could not bring myself to stand there taking photos of a 17 year old kid injured, devastated, and crying. It just seemed too cold and callous a thing to do.