Im against something like this too. A tank damaging themselves is counterintuitive and more to the point it will be poorly used all the damn time. DRK heal regeneration is a mitigation tool for them and is baked into their balance. Any skill that causes the DRK to damage themselves will fall to the healers to deal with.

That's ignoring the fact that it would in a hell of a lot of cases be used poorly in DF making DRKs extremely unpopular to heal.

DRKs are fine as they are.