I think it is generally a sign of maturity when a developer recognizes the flaws with their software and desires to improve them rather than piling on new features. Cynically asking "who wrote this shit?" is probably not a very mature way of expressing that, though. In my experience, finger pointing does more harm than good. If a particular developer is consistently producing bad work that is hurting the project, that should be evident by reviews of their new work - not their legacy code. IMO once code has passed review and entered master/trunk/production it should be considered the team's code - not an individual's.
