Thing is, in PA, registration is in fact against the law; the only reason their database still exists is because the PSP argued in front of the Supreme Court of Pennsylvania that their database was NOT a registry since it didn't account for pistols belonging to folks moving into Pennsylvania, nor those pistols that predated the database and have not changed owners. Thus since the database is inherently incomplete, it does not constitute a registry.
The problem arises when they use it as a registry, which they very often do, and they usually get away with it.