I don't think many would disagree with this principle, but I don't think his response qualifies as out-of-limit discourse.

I just read it as honest and accurate. He's not being a dick just for the sake of it. His thoughts sound exactly like what I would be thinking in his shoes. Knowing an actual user's moment-by-moment thoughts as he uses your product is invaluable. You shouldn't be encouraging him to bowdlerize that because it puts you off.