What right is violated when a privately run event chooses to ban a user from their premises for what they deem inappropriate behavior?

You can certainly disagree with any decision they make. You can speak out about it, and you can choose not to patronize their event. But no ones' rights have been violated. It's the Con's event and the final decision rests with them. Ejecting a person they deem a harasser is actually an exercise of freedom of speech and association, not a denial of it. They may be wrong in their assessment. But it is their right to be wrong.