>>People who do things like this INEVITABLY go on to harm humans. <<
I agree with that statement. But then, I think ALL humans harm other humans, and do so intentionally. The only one to ever live that did not was Himself hung on a cross. This can lead to “more” harm being done to others.
It depends on the age of the person. If the person is a young boy (if it was a girl, she IS a problem. No I am not kidding.) we should examine what may have compelled him to do it and correct as necessary. Of course, by “we”, I mean his parents.
If it was a young man, the damage may have already been done. Then again, if it was a “hick” that was taught to draw a very thick line between the value of humans and everything else, it may just show a mean streak or anger that was being taken out on an animal INSTEAD of a human they really don’t like.
This sort of thing is very complicated. Bottom line is that it is better that it was a kitten rather than a beloved cat or dog.
If

Bottom line is that it is better that it was a kitten rather than a beloved cat or dog.
???
The pain and fear felt by the animal is the same, whether grown or not, cat or dog. I don’t see the point here.