Sometimes users get hellbanned for no good reason. I was hellbanned for a few days and only noticed because I knew what to look for. I emailed info@ycombinator.com and they said it was an accident, and reinstated me.

I agree with anthonyb though, you should probably make sure they're not actually trolls before pointing it out.

The reason for hellbanning is https://news.ycombinator.com/item?id=5413912

"Adria Richards is an evil cunt.

SendGrid is a shit company that I would never want to work for."

Not exactly stellar material.

No need to inflict it on random passers-by though :P

This is why bans should start with a warning - hellbanning may be efficient from an administration perspective, but among other issues, without the possibility of appeal it's fundamentally unfair and prone to mistakes. (The ability of users to appeal after noticing something you're explicitly trying to hide from them isn't really adequate.)

But yes, this ban is probably deserved.

hellbanning has the fringe benefit that those who have been hellbanned aren't necessarily aware of it, which means they are less likely to register for another account.