All methods to block chatbots could easily accidentally go after regular users. And not just users being annoying, but your friends.
For example: You want to block a greeting bot. You make it so, if a players name is said within a few milaseconds of them joining, it bans. Now say your friend invites another friend to come play, and sends the message "Blah is coming." Just as he hits enter, the person joins. Banned.