tthakkar has a good post explaining the mindset of Macbeth. Literally translated, Macbeth is saying that since he's already killed Duncan, he's in big trouble whether he attempts to reconcile, continues to pursue his goals, or does absolutely nothing. Since he chooses to continuing pursuing his goals (which of course included the killing of Banquo and the Macduff family), he's telling you that he really has no morals left. Anybody who wanted to attempt doing the right thing would fess up to the murder of Duncan, accept any punishment, and do whatever necessary to try and regain some favor from the people of Scotland. Macbeth obviously isn't interested in the "right" thing anymore.