The concept is the following:

if you have committed to crime in the European Union, they will do everything to catch you at the boarder! (not a point in the US, if I'd kill somebody over there, I would just catch the next flight and bye bye)
The European Union knows who is coming and going. Nobody would tell you, you've overstayed and make a big stink if you can prove it with their owns stamps in your passport. (the US doesn't)
I think letting you in the country within 5 minutes in a reasonable friendly and non-discriminating, without taking personal data (other than necessary) makes up for taking another half minute to stamp your passport on the way out.