Well I've never been a "goth", but I did wear a lot of black when I was self harming. People who self harm often have low self-esteem and also suffer from depression and therefore tend to wear black and maybe not take a lot of care over their appearance. There are some really good studies being done into self harm. Harm minimisation and Camelot's study into young people and self harm are 2 that I have been aware of recently.