I think it might be a bit of both. There is something almost inherently appealing about the idea of those who fucked over everyone else finally getting what they deserve. And when you're a leftist, sometimes it feels like you are just helplessly watching as these ghouls actively make life worse for others in order to enrich themselves, and do war crimes in order to support the American empire, and all sorts of other evil shit that they are virtually guaranteed to get away with. And that just kind of causes those thoughts wishing the utmost harm on these people to fester.

But while this is a tendency we should actively try to check (in favor of this), I wouldn't go as far as to say that harm on their enemies is all "tankies" care about.