I can see two issues with this one: One is that there are numerous apps out there to hide one's IP. Hiding one's IP is one way people can open multiple accounts.

Hiding IP addresses isn't something I want to do away with entirely because it is extremely useful in the more oppressed and authoritarian parts of the world (and that's sometimes how information about those parts of the world get out to the rest of us.)

The other problem is that there are some platforms that use the first technique, but that tactic can be (and has been) weaponized against marginalized people by the same folks who send the threats.

I think one way to skirt around it is by doing what YouTube does (or something similar). It simply doesn't allow its commenters to use certain words, and will flag and warn you if you continue.