Can you name one example of law breaking that didn't taint the caster?
Time travel. No evidence at all that this creates a taint. Although to be fair, the question has not been specifically addressed.
And I would argue the calling an outsider "per se" is not black magic either, although dealing with outsiders is intensely dangerous and likely to lead to corruption through that interaction. But if you just called one up and kept it in the circle for an hour without interacting with it - and then sent it back -- it is hard to argue that this is black magic or particularly corrupting. It is CERTAINLY against the laws of magic.
Of course, if you want to get really philosophical, then all uses of magic influence the caster in some way. If those influences are in the not nice direction, you can call that influence (accurately) a taint. Using anger to fuel your magic taints the caster. I suspect using love to fuel your magic also has an impact on the caster. Using magic to harm someone probably causes a taint, although much less of one than killing with magic.
Black magic is a general term for really bad magic that is both very negative in an of itself and has a very strong propensity to strongly taint the caster. But it is certainly possible for a wizard to do a lot of magic that is "legal", but whose cumulative effective over decades is corrupting. Harry himself mentioned that his use of fear/anger/rage in battle has probably altered his magical nature over the years.
....and to give the other side example I forgot in my prior post. Drawing power from a very dark ley line can certainly badly taint a caster in the same was as dark magic, but that action is not prohibited by the laws of magic. It is still stupid, just not against the laws of magic.
