This is one of the only lesswrong posts I've ever read where I basically agree with nothing you wrote. You really should read the "rationality bible" though. Definitely before you keep posting here.
This sounds a lot like the objections CDT people were giving to Newcombs problem.
What leads people to even suspect that unicorns are sentient?
There aren't any clues that unicorns are sentient, so there's no reason why Harry should find QM killing a unicorn more thought provoking than eating pork.
Painfully murdering nonsentients to preserve one's own life is considered fine in almost all human cultures. In fact, painfully killing animals for fun is considered acceptable by most people, so long as the killing is done in a non-sadistic manner.
iirc, that spell wasn't homing, it just turned to the side at the end.
In GoF they had to set up an apparition-is-allowed-zone at the end of the maze in order for the portkey to work, which is why Crouch had to wait until Harry had won the cup instead of just turning a piece of silverware into a portkey or something.
I used to think like this, but recently I've updated into seeing everything as potential foreshadowing.
I have no idea how I managed to miss that.
Prediction: Harry will have to make an unbreakable vow not to use the elixir of life himself in order to get the Philosopher's stone from the Mirror or Erisid