Uh... no they don't.  Can you tell me how your puny little door lock will stop my foot?  The door frame to your house is made of wood... oh what's that?  You have a metal door frame and a reinforced slide on the door?  That doesn't stop a 40lb door ram (there's a reason police use it to bust down doors).  But seriously, why bother with a door when there's 1/8" of glass keeping people out of a structure?  Any handy rock will take care of that problem.

Subtly you say?  The lock picking link above is good... a credit card works fine unless you have a deadbolt on, then just resort to lock picking.

I'm going to make a guess here: You think that having more lights (streetlights, porch light, etc...) in your neighborhood is a good thing and makes your neighborhood safer, too, right?

Door locks do nothing but keep honest people honest.