Agreed. Had my bike taken while in college. My jackhole roommate left the side door to the garage open and unlocked. My bike was the nicest of the five to the homeless man that took it. .
Best part, I got it back 3 days later. At a football tailgate (Michigan State University), I recognized my bike, with a kickstand it did not have before, fifty feet from me. It was adorned in plastic bags and empty cans (With a ten cent bottle/can deposit in Michigan, a dude can make a few bucks in empty beer cans.). I waited until the new owner came back, demonstrated that my key opened his u-lock, spouted a baseless threat and I then told him to get on his way. One missing bike returned with an new kickstand I didn't want or need.
Wouldn't have happened if I'd locked it.