Oh, and Harry didn't even ask whether it might be possible to substitute an animal for the human sacrifice, or make a portrait of the caster and use that as a substitute, or Transfigure a rock into a copy of the caster (under heavy precautions, of course). He displays an irrational degree of revulsion at the idea of killing people. One gets the idea that he would let five die in the trolley problem.

I got the same impression. Harry!MoR in general seems to be very good at giving rationalist speeches (and internal monologues) but rather poor when it comes to actually thinking rationally under this kind of pressure. He may not let five die in the trolley problem when it is presented in a nice philosophical form but it wouldn't surprise me at all if he encountered an analogous problem like we see here and completely fail to even look at options once he hits an emotional roadblock. It would make me hesitant to trust him.