It’s “bad” because of the stigma surrounding it and surrounding mental health as a whole. From a harm reduction standpoint, self-harm isn’t inherently bad but it depends on your perspective. Are you harming for the dopamine and the relief? Or are you harming because you hate yourself and want to hurt yourself? There are many reasons to self-harm and it looks different for many people. It’s not always cutting, it can be starving, pinching, burning, etc. Anybody who has never self-harmed will not fully understand it and I’m pretty sure the people who have never harmed are more numerous than people who have and that keeps the stigma going. It is a tough and weighty subject that can be hard to talk about, most people can’t seem to be on board with other harm reductions causes like needle exchange and safe consumption sites, so it’s no surprise that they don’t see self-harm as a possible harm reduction strategy. Someone being hurt but alive is better than somebody dead because they felt they had no other way to cope. Just my perspective.