Avoiding Darkness Induced Audience Apathy In Horror Genre

As an amateur horror writer my most commonly weaponized trope is Primal Fear and basically any trope that is considered immoral. The latter of which I have certain troubles with due to fear of causing Darkness-Induced Audience Apathy. I mean, a bit of murder or cannibalism probably won't do much, and I admittedly won't pull off evil vs evil morality very often. However, I do have plans for a particular short story that will include evil vs evil morality.

So what's the best way to do this then? I already have an idea on how the story could progress. I could start out relatively idealistic and make it gradually more depressing as the thing goes on, but saddening enough, that's all I have.

As a horror writer too I think it's merely the case of getting the reader to care about the people being victimized.

In the early Friday movies, you wanted the protagonists to survive.

They weren't just meat for Jason.

Yea, I get that sorta logic, and it (arguably) pretty much applies to all fiction these days.

But the issue here is that all of the characters start doing immoral stuff. To varying degrees of course, but it is evil vs evil for a reason.

IMO humanization beats virtue every time in terms of characterization. If you can make said characters relatable with understandable motives, then they can be as evil or as nice as you'd like as they'll still be compelling.