I’m going to want to stop him.
Good, do that.
Anarchy is 'no rulers' not 'no rules'. If someone is going to do something harmful for the community, you don't just let them. You are actively incentivised to stop them, because it's your obligation as a member of the community.
Contrast that to today's system, where if someone wants to release factory run-offs into the local water source you can't stop them and they'll bribelobby some politician to let them do it, while arresting you for protesting it