Why exactly is it controversial? That is the exact emotion that visiting Auschwitz is meant to evoke. Not all art should be joyful.

(edit) Even if the picture is about kids being sent to '40s Auschwitz to work, suffer, and die - that is what happened to real people. Don’t look away. The gut-punch feeling is what you’re supposed to feel and remember when people bring up fascist rhetoric. Again, not all art should be joyful.