And it does not matter: in the US and most civilized countries a police officer is supposed to have a reasonable suspicion before they start invading someone's privacy.
The idea of someone running warrant checks on the basis of a broken tail light is antithetical to notions like the presumption of innocence and right to privacy.
Hm, there's definitely a line somewhere. I'm with you in that I don't think cops should be able to demand ID and run checks on random people simply out and about in public. Broken tail light? Not sure. Speeding? OK now you're breaking the law and arguably creating a public safety threat, but probably not going to be arrested. DUI? Now you're in misdemeanor territory at least. When is it reasonable to check if you're also wanted for something else? Maybe when you're booked at the jail?
Census workers aren't expected to check for warrants, because it's not their job; I'm advocating the same for things like speeding enforcement.
Philando Castile serves as a good example.