It's interesting that you would draw the line at "photos of Hiroshima or liberated nazi death camps" because this is exactly what I was shown in school (at age 13 or 14) in history lessons. I assume the goal was to shock in order to remember that yes, the holocaust really happened, and it is our responsibility to not let something like this happen again (this is in Europe by the way). I know my friends were also into looking at gore pictures online around that age, even if I personally never felt the need/want to.

But what's for sure is that the images of mass graves and emaciated bodies are stuck in my mind probably forever, and I don't think it's a bad thing as long as it came with proper guidance. It's not the same thing to see them in school with a proper explanation and to stumble upon them by randomly clicking around online on your own in your room.