Trigger warning for, obviously, self-harm.

There's a huge chasm between a mental illness diagnosis (which self-harm is very likely to cause, especially in the US where you need diagnosis other than "ain't quite right - not otherwise specified" for insurance) and actual repercussions. Members of online support groups report that their psychiatrists either treat self-injury like any other symptom (asking about it, describing decreases as good but not praiseworthy) or recommend they stop but do not enforce it. If it gets life-threatening it's treated like suicide, but that almost never comes up.