yet another analogy
Try this one on for size. You have a Porta Potty (portable outhouse/bathroom) on your sidewalk. Do you expect someone walking by, or your neighbors outside not to use it (if they need it) when you leave it with the green sign saying open. Now if you put a lock on that out house people breaking the lock would be breaking in, or if you just tie it closed with a wire, that would be like using the default password for your router. Putting the Porta Potty in your backyard or in the garage would be like not broadcasting your SSID.
Porta Potties are a common convenience when there is no easy way to have a bathroom close by, you can look at WIFI as the same, its a convenience. If they dont want you in, they can disable the broadcast of the SSID, password protect it, among many other things.
I am going to put the default password on my router and any access done by cops will be reported as unauthorized access to a secured network, of course ill put a sign in my window stating the wireless password so that others can see it, In small print it will say that I grant access to everybody except law enforcement personnel.