Statistically, the correct answer is Detroit. But Florida's larger cities aren't exactly safe - especially Miami and Orlando. Where I live in Florida has a relatively high crime rate, but it's not too dangerous. In most places you'd feel safe leaving your door unlocked at night. Although in Jacksonville, just a few miles away, I certainly wouldn't advise that.
People do that?
I often leave the door unlocked even if I go out. I wouldn't want to live anywhere I couldn't do that.
Why even have a lock, then?
Well, obviously I lock my door when I'm gone for extended periods of time...
This is something you and I have in common. My family don't lock our doors at night or if we're just at work or doing errands, but we do if we go on a vacation or something.