If that's the case, why go through all this hassle? Simply use IRC with SSL and you have exactly the same level of security. As long as you trust the server, you are fine.
I think there's still value in hiding the conversation from the server even if you must still trust the server to not behave maliciously. If some three-letter agency contacts the server operator asking for a back channel to listen in, he or she could respond that it's not possible without malicious intent towards a user:
http://www.macobserver.com/tmo/article/apples-imessage-encry...