What's the function or basis of law, or even cultural enforcement? And how can we know that a certain system is truthful and just?

To my reasoning, it must be shown that infringing a certain law one not only gets worse off as an individual, but that if all other persons committed the mistake then they'd also be worse off.

Again, it must also be shown that no good can come out of such an infringement no matter the context, or in most cases.

Take murder for example. It passes the criteria. But what about 'apostacy'? Like in this case http://m.aljazeera.com/story/201451455639303457