it's completely appropriate to feel revulsion at the idea of killing the one person in the trolley problem... as long as you feel five times as much revulsion at the idea of letting the five in the trolley die.

That's what I mean by an irrational degree of revulsion. As far as we can tell, it doesn't even occur to him that a Horcrux trades off a finite life for an infinite one.

creating a Horcrux requires genuine hatred and malevolence.

There are mind-altering spells. The clinic doctor can make you evil enough to cast the spell, and then do Finite Incantatem once the process is done.