I understand the value of the Peer Pressure badge. If a post has a negative score, it means it is not a valuable one and deleting it by oneself cleans up the forum. But why give a badge for deleting one's post with a positive score? Or do I miss something about the working of the Disciplined badge?
Sometimes, score doesn't reflect actual post quality. Maybe an answer got upvoted and then you realised it was wrong. Deleting poor content even if it loses you some rep points is perhaps even more praiseworthy and community-minded than deleting poor content that's downvoted, which could be just to avoid losing the rep.
As for Peer Pressure and Disciplined, they both have good motivation. One teaches that you can remove bad content; the other is to encourage removing bad content even though you'll lose some precious Official Reputation Points.