Might not be popular but you dont want to restrict that type of stuff in tech, because people very quickly and easily find ways around it, usually by using new similar words that call back to the prohibited ones.
This is an area where moderation is key, and I think people might need to reconsider who they allow to send them direct messages. Especially I expect there to be a better way to vet someone who is trying to directly reach a stranger.
If you are literally going to open your door to the whole world some bad stuff will fall in, but you dont have to let them into your private areas just because they made it in the front door.
Trust networks are another idea, essentially verifying new people through acquaintances.