Why is self-harm considered bad?

Because it involves physically harming oneself, but mentally, a lot more harm can be done than is taken note of. Physically self harm can normally be seen, mentally, it can't.

Self harm is considered bad for a number of reasons. Firstly you are causing yourself harm, which is a sign that you are struggling emotionally. This needs to be addressed. You risk hurting yourself seriously, infection and even accidentally killing yourself. Self harm can also be seriously addictive which is another problem in itself. You can permanently scar yourself. These are all things to take into consideration. Some people might say that self harm is attention seeking, or manipulative - this is untrue but it is a perception held by some. At the end of the day, self harm is NOT healthy and if this is something you struggle with I urge you to seek help as soon as you can.

Nothing is always either good or bad. There could be grey, too. Sometimes, it's just the situation you are in, due to which you end up doing things that you know aren't good for you, but you do it anyways. Coz it probably gives you a temporary relief. But, you have to remember it ain't a permanent solution

Self-harm is considered bad, because the person gets hurt by doing it. Hurting somebody is never something good and especially self-harm is bad, because you are hurting someone deliberately.

Because you are harming your body, which isn't a good thing. Anything that causes you harm is no good.