And that wasn't the starting point? What a joke!
> We would never allow a violent criminal to attend LambdaConf.
Yes, you would. You'd be sued if you didn't. They did their time and (presumably) got out or the question would be moot. If they (or anyone else) threatened someone, see the next point.
> There is always a line. There must be one. The question is, where do we draw that line?
I've run conferences for years where the only policy of that sort is that we won't hesitate to call the police.
It's worked perfectly because if someone follows someone else to harass them that's illegal despite the subject matter. Harassing someone for liking the wrong pokemon is just as actionable as harassing them because they're the wrong gender. If the person isn't harassing anyone they're free to their opinion no matter how odious.
The police are very helpful in explaining "a disturbance" and how someone is creating one!
And here's the answer to threats, violence, etc. They get arrested. Not expelled. Not shamed. Arrested. Treat it like you'd treat random street crime and have them arrested.