People who self-harm often run into some pretty strong reactions. Some people seem to think it is okay to give a look of disgust after noticing the tell-tale markings. They also completely change the way that they treat that person, like their self-harm has anything to do with whether they are a good person or not. I am here to say that it has nothing, absolutely nothing to do with what type of person they are. And furthermore, it has nothing to do with you. This is entirely a personal battle being waged because of such internal pain that they are trying to escape it by creating external pain.
I beg you to understand that someone who can inflict that kind of pain on themselves is in crisis. Think of the amount of inner pain that it would take for that kind of outer pain to feel like a release. If you cannot even imagine it, you should count yourself blessed not superior. Stop heaping salt into their wounds with you disgusted looks and stop grinding it down with your hurtful disregard.
That type of behavior toward another person should be unacceptable!