I don't believe selective enforcement of the law is unethical, if enforcement of the law would be immoral. However, criminalization of acceptable behaviour with

I don't believe selective enforcement of the law is unethical, if enforcement of the law would be immoral. However, criminalization of acceptable behaviour with an aim to selectively enforce it for some other motive may be immoral. E.g. if you wanted to imprison a particular race, so criminalised something acceptable which everyone does, and more aggressively policed that race.