There are several problems with this passage (its not a direct Platonic passage, but rather a theme): "Good people" intrinsically follow the law and therefore do not require laws. That is, law abiding people do not need laws to tell them what to do. This is preaching to the choir. The prerequisite for this state of affairs is that the laws are virtuous.

"Bad people" find ways around the law, once again, people who are not law abiding, by definition, break laws or find ways around them. Once again, we are assuming that the laws are benevolent and virtuous.

The theme adds little value in my opinion. It's a circular argument. About as useful as: Good people do good things, and bad people do bad things.

The more interesting aspect this brings up is the interplay between the laws of society, personal ethics, and the relationship between legality and morality. Plato's Republic dives deeply into this area underpinned by Laws authored and enforced by a benevolent king dictator for life.