There have been ships capable of navigating the high seas, 5500 years ago!
Er is that the point of view of academics whose closest contact with the ocean is when they take a bath? Yeah I'd like to see one of those ancient vessels in an average storm. I have sailed, and believe me you quickly realize how easy it is to visit the bottom of the ocean.
Just because they didn't, doesn't mean they couldn't. Actually, it probably does mean that. While there is evidence that ancient peoples were capable of incredibly long trips - the proof of which being the colonization of Pacific islands by people sharing Asian genetic markers, those trips were probably the exception rather than the rule. People tend to take advantage of any activity that is fairly simple and fairly profitable. If it was so easy to cross the oceans, there would be much more evidence of contact between civilizations in the old world and the new. I'm not an anthropologist, but AFAIK besides the Phoenicians and the Vikings, there were not many other powers that dominated the waves.
Bad analogy. There is nothing illegal in the US about owning a rip of a DVD. In fact, the law specifically states you are allowed one (1) copy for backup purposes. Unless you're downloading stuff in front of the customs officer, what is he going to do? Of course if your computer loads utorrent when started, and you have files on your HD saying stuff like "thanks for downloading warez at xxx.net site", then that might be incriminating enough - IANAL. But just having the rip? Rename it to "SomeMovie(Backup).avi" or whatever and you're 100% covered.
Using your example, it's more akin to you crossing the border while under the influence of heroin. So long as you don't act in an intoxicated/disorderly manner, there is no law against being high. The laws cover possession, distribution and sale.
Thus spake the master programmer: "After three days without programming, life becomes meaningless." -- Geoffrey James, "The Tao of Programming"