Quoting the entire message is not desired for the sake of avoiding noise. And neither is it required because when you reply to a post, your reply is linked to that post, so it’s evident what you’re replying to (with one exception: with the default settings, a reply to post directly above is indistinguishable from a reply to topic).
I highly recommend using the quote button to selectively quote exactly what you are reacting to. This is one of the key features of discourse that distinguishes it from other forum softwares! The only problem I see with it is that once you got used to it you have to endure physical pain whenever you have to use another forum software that forces you to quote everything (or doesn’t allow quoting at all).