Now this is simply drifting off into absolute absurdity, wideawake. Neither Mexico nor Canada (simply to take the two most obvious and geographically pertinent examples) allow U.S. citizens to enter said nations at will -- flagrantly flaunting their own legally established immigration procedures, mind -- and then to stay, indefinitely, in direct violation of their sovereign laws. Plainly, neither of these are [*kaff*kaff*] "police states"; neither then, demonstrably, is the U.S., in doing precisely the same.
In all candor, FRiend -- no needling or sarcasm intended (honest) -- I'd recommend stepping back from the keyboard for, say, half an hour or so, and re-thinking this particular line of argument. It's a non-starter. ;)
Yes they do.
All I need is a valid US passport to visit Canada or Mexico at any time I want. I can apply for a job in either country and receive a work visa - and eventually a residency document - in either country. The employment part is more difficult in Mexico depending on what job you're trying to get, but if a professional firm in Mexico City wanted to interview me for a position, I could be in their offices tomorrow, no problem.
Border controls are for keeping out criminals, the insane, the communicably diseased and people whose presence alerts suspicion.
It isn't for keeping out normal people who want to visit or work.