Why include it? It's threaded!
You've got the opportunity to do just what you want with tools, autoquote while replying.
Personally I hate auto-quoting of whole messages, particularly when people put their replies at the bottom so I have to scroll through the question that was asked looking for the answer.
I just use right-click and open in new window on the original message, so I can remember what I'm replying to. Might be senility setting in :)
Then if someone asked many questions in one message, I might have to quote
short bits of their message to make my reply make sense.