I'm a relatively new DM (started over lockdown), one of my players wants to use his 30 year old female halfling as a honeypot in a "to catch a predator" fashion which would obviously require me to portray the predators. I've told him multiple times that I'm not comfortable doing it but he keeps pitching it and now another player has joined him in asking for it. Should I just do it once to get it out of his system or stand firm and keep refusing?

Edit as I've got a lot of comments asking about it: predators of that kind have never existed in my world so he's effectively trying to create the predators in order to catch them