I don't understand why self-harm is bad

I have been self-harming for about a year now, I have been caught many times, I have told friends, family, acquaintances and they all tell me it is wrong, they ask me why as if I had to have a reason, but I just do it because that's the way it is, even when I feel fulfilled it makes me want to do it and I can't understand why it's wrong. Cutting myself feels good, I don't cut myself so deep that I risk my life, I don't show it to people, I don't bleed to death, and it won't kill me in the long run just by continuing to cut myself. It's not like smoking, which is so accepted, even though it kills you slowly and condemns you to terrible diseases, why do people look at me badly for cutting myself but tolerate smokers? I'm not amputating my leg Or something weird like that, I'm just making cuts with a leaf that will heal in a week, come on!