The common law process is by its nature an appeal to tradition. If there is a governing principle in our society, it's "this is okay because we've always done it this way." Yes, in a way it's ridiculous because we end up arguing about what people thought about border searches in 1789, but that's the nature of our society. We don't come to a consensus to solve problems, because we never agree on anything. Instead, we litigate them and grudgingly accept the outcomes. That's why court cases feature so prominently in our culture (Brown v. Board, Roe v. Wade, etc). Non-Americans, understandably, usually find it utterly bizarre.

Re: border searches, I'm not well-versed so I'll just point you to the wikipedia page: http://en.wikipedia.org/wiki/Border_search_exception. Long story short, it still has to be reasonable, it's just that the bar is lowered because you should expect to get searched at a border.