Some laws are just not really enforced. You don’t ever hear about police enticing “criminals” to jaywalk against a red light, or buy a gross of prohibited bottle rockets. So when cops are spending a disproportionate effort on enforcing laws against crimes that are mainly perpetrated by poor people and really don’t harm anyone else, I have to question their motives.
Yeah, it doesn’t address the legitimacy of police stings in general, but it is tangentially related. I think drug and prostitution laws are generally a proxy for locking up certain undesirables who are otherwise innocent and law-abiding. And I think that police stings are part of that effort.