Although it goes without saying that builders who make roofs that cave in aren't going to get a lot of business.

I think where codes can sometimes come in handy is allowing some input by professionals into work done by amateurs. Being "not to code" can give local authorities the clout to make a person change something he has done himself that may not be safe for people other than himself. Kind of the regulation equivalent of making a person turn his lights on while driving at night. Reasonable, even for a libertarian.

Unlike with a professional architect, there is no serious market pressure on an unskilled do-it-yourselfer to do it right. It's not like he's looking to impress any other customers.

There was a fire near here where some of a family died. They had built a room onto the outside of a house. The room had no other outside exit except back into the house, and then the fire started.