Agreed, nobody wants to live in a police state, but the prospect of choosing to talk to a cop about your OLL is a situation which can happen, despite assertions of rights and any preventive measures taken. OLL owners may want to practice for that time to avoid a needless arrest, to educate the police, and end the matter uneventfully.
If you clam up, you increase the cop's index of suspicion and maybe therefore your probability of arrest. Cop sees an 'illegal' rifle, the owner won't explain away the illegality, so unsurprisingly the cop makes an arrest. Yes, you're asserting your rights the whole time, but choosing to clarify the cop's mistaken understanding might have prevented the whole incident. You can go about your business without the hassle and expense of arrest and defense. I'd rather buy cases of ammo than buy time inside and release from the justice system for the sake of proving a point. Think it out before hand what you're going to do and why, and prepare.