Unintended Consequences:

I've argued that congress should make no law to control any aspect of software or the internet, for the simple reason that it's impossible to anticipate the effects such laws will have, especially since the actual use of each piece of software can be so different from the intended use.
However I was myopic. Unintended consequences are simply the order of the day, and one must be humble about claiming to know the implications of any change. I've been reading about how car thieves who used to hotwire cars now steal them from their owners at gunpoint, since it has gotten a lot harder to start a car without its key. And there was the awful case of the gang who chopped off a car owner's finger to steal his Mercedes, which could not be driven his fingerprint.
And here's a remarkable unintended consequence: Mexicans used to sneak across the border to work as illegal aliens for awhile, then sneak home to their families. But it has gotten a lot harder to cross the border, so now entire families sneak over and live here illegally - permanently - in order to minimize their border crossings. The Tucson Citizen has a report on this, Illegal Migrants staying longer. To paraphrase Abe Lincoln, you can fool all of the people some of the time, but once they think of an angle, they'll fool you right back.