Even if they are sapient, it might not have the same psychological effect.

The effect of killing a large, snarling, distinctly-not-human-thing on one's mental faculties and the effect of killing a human being are going to be very different, even if one recognizes that thing to be sapient.

If they are, Harry would assign moral weight to the act after the fact: but the natural sympathy that is described as eroding in the above quote doesn't seem as likely to be affected given a human being's psychology.