What the cop is doing might not be illegal, and even if it was he's unlikely to get in any trouble. ...but it's a huge violation of one of the main concepts behind the bill of rights and to a lesser extent the constitution. Those who created those principles were trying very hard to prevent the gov't and police from poking their nose into your business unless they had a damn good reason that they could prove in court. By your logic, why not eliminate the 4th Amendment entirely? If they could search and seize at will, they could probably find a reason to arrest someone, right? So why not?.. because those that were willing to fight for freedom found it intolerable.