Horror can be subtle or in-your-face and I can relate to deciding which to use with supernatural fiction...Violence can be a very real controversy when we must decide how to use it, if to do so, when, in what way...
I can imagine having written a story about a nut dressing like the Joker and attacking a movie crowd. That would be a great story and it could go into the reason he does it and the people there who are heroic and who are cowardly....it would be a good vehicle to tell a story. HOWEVER...my God, it happened! The writer, if he had written such, would feel terrible and be raked over the coals and probably threatened, It is very possible and very controversial as we can all understand.
I think we, as horror writers, don't design or invent the violence, but we simply delve into the human mind and see the possibilities of some terrible things.
A man tells his friend he wants to be on an airplane that is hijacked but that lands safely in the end and the bad guys are caught and no one is harmed.
"How horrible! You would be terrified." The friends says.
"Yes, but it ends ok and then I won't be afraid of that anymore because what are the chances of me ever being on 2 hijacked planes?"
Horror sells because once you have seen or read it, what are the chances you will ever be in that spot again? You have seen the demons and escaped. In some ways, when we read about violence, we are carrying a rabbit's foot after that...a talisman of protection because....what are the odds?