But if humans deemed this optimal, it would not be possible to have a "rule of law" system, where there are definite laws, and people can know when they're breaking them, and which disallows favoritism.

The consequent here is independent of the antecedent - I don't think the system you describe is possible under either circumstance.

While it may appear that it's a chance to shift utility toward people you like, your deciding to do so has broader implications.

So at the very least you should say upfront that you regard it as optimal to nullify unjust laws, which will get you tossed out of the pool but otherwise unhurt.

I'm not seeing how this follows without some additional value judgments. You're basically saying "Widespread nullification would fuck up the legal system, so don't do it", instead of "... so beware of the trade-offs involved".