I'm just talking from my own experience... but I think that most people probably start off with being "safe" while Si'ing, but eventually, that can progress to more damaging acts of SI. Left uncontrolled, this can turn into an addiction (as others have mentioned), and if you're not careful, you can seriously do damage and make irreversible scars. And not only does SI hurt you personally, but I know that I have hurt other really important people in my life through MY SI. One woman in particular was so concerned/scared that she completely backed off and is no longer in my life.
It wasn't a dumb inquiry... no need to "shut up", keep asking questions and pursuing your answers. The more understanding you have, the better chance of NOT si'ing there is