Theybare fascinating. Humans often have morbid curiosities. It's okay to have them or not have them as long as you're not actually murderinh or harassing victims and their families.
ᴳᵒ ᶠᵘᶜᵏ ʸᵒᵘʳˢᵉˡᶠ

It's not sick, quite the opposite. It's actually baked into us as humans

Being in the military is not murder. Killing for a cause though sad is not the same thing as killing for fun.

Murderers are not fascinating. There is nothing special about them. Anyone can kill someone. Anyone can destroy something. It takes no special ability whatsoever.
If that's true, then why don't more people do it?
Most
can't
do the things you mentioned. Murderers are fascinating in that other than having little remorse and guilt for their victims, they courageously lack of fear of life-altering consequence.
There's the realistic, practical aspect that no one thinks about:
Me, murder someone? I can't even get out of bed on time for work. You think I'm going to risk having to get up at 5 AM to go to the police station? Hell no. I want to sleep in. Then, having to clean up the blood stains off your hand-stitched Boca do Lobo sofa. No, thank you.
Most people generally don't want to leave their home, risk waking up at 4 AM for the rest of their lives in a cell on an uncomfortable cot without a box spring.
If anyone could murder, then more people would join the military. You'd get most the things you'd get with murder except it's a positive on a resume: leaving home for an extended period of time, sleeping in a place that's similar to a prison but slightly better conditions, and the potential opportunity to kill people legally. If most people aren't willing to do this, then a significantly fewer number of people would murder.
Never lose your desire.

The fascination people have with politicians and CEOs who are mass murderers is sick.
Melton1 Wanted for Pedophilia:
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https://m.youtube.com/shorts/Zjxk307CND0