People read dark fiction for the same reason they ride roller coasters.
It’s a simulation of danger without anyone actually being under threat. It gets the brain worked up, releases a bunch of adrenaline into your system, you experience a whole rush of emotions and excitement and fear; but a safe kind of fear, where you know the danger isn’t real and there are dozens of measures in place to protect you. And then it’s over and you can get off the ride.
That doesn’t mean everyone is obligated to ride roller coasters. I, for example, am scared of heights, and most coasters are scary for me in a way that isn’t fun. The fear isn’t that I’ll die, the fear is of experiencing more of the ride and thus it’s not a safe fear, because it’s real and I have no control over it. As such, I don’t ride large roller coasters. But the fact that large coasters are not mentally or emotionally safe for me to ride doesn’t mean they should be illegal, or that there’s “something wrong” with anyone who enjoys them.
Similarly, sometimes accidents happen. Sometimes people have conditions they don’t know about until a coaster aggravates them in the worst possible way because they didn’t know to avoid it…and that’s no one’s fault. People have died or been injured in coaster accidents, and those accidents are pretty much always the result of human error, carelessness, laziness, or poor communication. It’s the responsibility of the amusement park to make sure that basic safety features are built-in and maintained–or at the very least (mangling the metaphor somewhat because this would obviously be illegal in real life) to make it clear that those features don’t exist! I feel like most people would avoid a ride clearly labelled “HAS NEVER HAD A SAFETY INSPECTION! NO RESTRAINT BARS! RIDE STAFF HAVE NOT BEEN TRAINED AND THERE ARE NO EMERGENCY SERVICES ON-SITE! OPEN FLAMES!” but if you click on a fic clearly labelled “author chose not to use warnings” you know the risks and they’ve met their obligation to warn you of them. And sometimes the people providing this content don’t perform that basic due diligence, and people get hurt as a result–but that’s on those specific bad actors, and doesn’t mean we ban all roller coasters. It also doesn’t mean every single ride operator on earth should be tarred with that brush, especially when they’ve openly spoken out against such practices! Furthermore, if you KNOW you have a heart condition and willingly get on a ride that says it is not safe for people with heart conditions, you cannot then blame the amusement park!
What makes roller coasters safe for me? Well, for one, the fact that I’m an adult now so my family has finally stopped trying to force me onto them.