It is just too easy for those viewers of photographs to pass judgements on them, while sitting in their armchairs sipping on a glass of cognac. By its nature, a still image bound by two pairs of parallel lines can say a lot, but at the same time leaves out a heck of a lot more; I believe Carter was well aware of the repercussions but chose to click the shutter, like countless photographers in such appalling situations before him.
This reminds me of what happened to me. During 1989 I was working in Hong Kong when the Tiananmen incident was gathering pace. Nearly all the photographers, photojournalists and reporters I knew took the first flight to Beijing, and some actually asked me why I was staying put. I said, "don't forget Paris Commune" but it fell on deaf ears. Needless to say the secret services repeated exactly that, using the photographs to add to their wanted lists. While there have been a few fellow photographers who started their careers in that occasion, I made the statement of not photographing, and at least, I can sleep at night.