> How would one prevent continued harassment in your system?

Probably depends on the form the harassment takes. In this case, you can report bullying to whatever social media platform you're using. Minors in particular have extra protections.

People don't have a right not to be bullied, but they do have the right to choose their associations and to choose the situations in which they place themselves.

For instance if you are a member of a gym and are getting bullied at the gym, you can complain to the owner. The gym owner can remove the bully. If the gym owner refuses to do anything, you can take your business elsewhere.