The Catholic answer is that sin is not an arbitrary list of dos-and-donts. Rather, the things that help a human flourish are good, whereas sin is always, one way or another, destructive of self. In other words, sin is built into what it means to be human.
This is a statement (perhaps overly simplified) of the basic principle underlying natural law.
If I own (and drive) a car, I need to change the oil regularly. That means that the injunction in the owner's manual to change the oil is not an arbitrary imposition--it's simply what's necessary to keep the car running. Likewise, sin in one way or another always leaves us running less efficiently, makes us less human.