Common law countries rely on the courts to declare what the law is, and the doctrine of precedent gives the law its certainty. A legal system which is uncertain is grossly unfair.

However, a legal system that is bound by precedent becomes rigid and unadaptable, and injustice can arise there too. Thus, we have equity - the gloss on common law - which redresses such injustices by issuing injunctions to prevent the unfair consequences of enforcing a legal right.

Statute (or the Constitution, where you have one) overrides common law and equity, because the legislature desire the law to say something in particular, and it cannot be left to the judges to say it (if they ever get round to trying a case that involves the point of law in question). So, I don't think fairness comes into it. Whether it's a fair law or an unfair one, if the lawmakers want it, they'll have it. And the judges must adhere to it.

For example, is it fair that bankers can pay themselves enormous bonuses while their company has to be rescued bu the government? Why not? If their contract entitles them to the bonuses, they should have them. But many people - even in USA - would like to see a law passed to prevent these fat cats getting any more cream.

Neither common law nor equity would allow that.