You might need to recalibrate, or face the fact that you're not seeing what you "should" be seeing. I put that word in scare quotes because what you should be seeing depends partially on the video. A serial killer might want you to see their own perversion, or the entertainment, so to make you into a consumer of the video like any other online video. Or the video might be making an example of someone, so makes you into someone who respects a kind of power or threat, making them into a mythical force (like Mexican cartels have successfully done).

But that context should be contextualized more broadly. Why I think it's important for people to watch those videos is because it allows you to see death--really see it, insofar as you can see it in a video--WHILE seeing human beings both dying and taking life. You should be seeing the potential for brutality in a person (any person) and the absolute relatability of suffering in the end of life.

So in other words, it depends what doesn't bother you anymore and how it doesn't (being "desensitized"). It might be that you mean you don't recoil from the sight of blood or taking of life anymore. That's not necessarily good or bad. But if because of that you're also not seeing the person taking life, or the person having their life taken, you should stop watching. Being a passive consumer of death is part of what inspires the content creation itself, and the inspires consumers for it as content.

In my view the videos are important to look at because the west has almost absolutely eliminated real death from everyday life. But there is no life without death. And there is no understanding life (people, things, beings) without understanding the potential life-taking in others, and how others can and do have their lives taken.

In response to something like that, especially from someone who doesn't watch this stuff, you'll often hear that they "get it." And yet they simply can't watch those videos. Not only do they not get it, they can't see it. Some people can watch the videos, but that also doesn't mean they "get it" if what has happened to them is, in a sense, a form of shock from sight of it. If you feel numb to the videos, that might be the case.

It's a long way to say that, but I think it's important. These videos must be watched, but they also can't be consumed.