So you are spamming anyone who joins the chatroom.
I'm puzzled how you could even think that assaulting anyone who joins the chatroom could be appropriate. It's bad enough when people do that manually, but automatically‽
Any auto-greet message is spam and that makes the auto-greeting bot a spammer. Banning that bot was appropriate. Letting the bot run was not appropriate.
A bot should never ping a user who didn't opt in.