The community [doesn't like discussion in the comments](http://meta.stackoverflow.com/questions/95937/why-must-we-avoid-discussions-in-comments/95938#95938):

 - There shouldn't be useful information hidden in comment threads, it should be visible in the Q&A.

 - We don't want noisy chats between our Q&A, that's what the chat is designed for.

An explanation from [my attempt to have more descriptive messages](http://meta.stackoverflow.com/questions/96493/can-we-have-customized-verbose-descriptive-automatically-move-this-discussion):

 - A comment is a remark expressing an opinion or reaction on the question or answer.

 - Comment threads aren't meant for chatting, conversations and discussion.

 - If there is a conversation where the questioner is replying back-and-forth on either comment or answer to resolve his problem, the question or answer should instead be improved...