This article from ScriptMag.com gives some insight into how to write a gruesome scene without alienating your audience. Here’s an excerpt:
If you want to write a scene that depicts the horror of violence and want us to identify with the victim’s suffering rather than with the villain’s sense of power and control, the best way to do this is not to make the violence all the more visible and graphic. The trick is to create empathy for the character before the violence occurs, and then depict “the act” in such a way that we are not compelled to emotionally disengage and detach.
There’s really no way around it. Put “blood and guts” on a movie screen, and you may end up making a movie that appears to be a cheerleader for violence, and your “message” about how bad violence is or how abused and exploited the victim is, can get entirely lost.
Remember that the violence we can see in our mind’s eye is far more graphic and powerful than anything you could ever show us. If you, as a screenwriter or filmmaker, can inspire our imagination, this will make us engage with your movie and its hero rather than turn away.