There is no exact measure in this. A violence story to me may be a lame story to another, and vice versa. If I said it is okay to have violence providing the story is tastefully done, then one person's opinion of tastefully done is different than another.

A few years ago, Threshold, one of the larger Los Angeles chapter of BDSM group has a member who left because some members post actual violence slavery story and these members posted the story just like any other gossip. That female member left the group and post a message saying "hey, these are not fantasy, they are reality. And quite frankly I agree with her.

On the other hand, if violence is posted in a fantasy novel, I would like it all depends on who the reader is to determine whether it is tastefully done or not.