I doubt alot of harm could be done from users accidentally accepting chat sessions.

Not true - There was a "mIRC exploit" (DoS against mIRC) involving DCC chat sessions which could be triggered just by opening a chat session. It would freeze up mirc and force the user to quit without being able to perform any more actions

That bug has now been fixed (it was fixed way back in the 5.x series iirc) but it shows that accepting a chat session can be harmful