I'm a country mouse. Our door didn't even close properly, never mind lock.
It was a struggle when I went to uni to learn key discipline.
When living in a city for a while someone came in through my unlocked front door while I was in the bath and burgled some things. The insurance paid out.
I still leave my front door unlocked when I'm in, and unlocked at night too.
Where I live now the risk of burglary is significantly lower than the risk of house fire. The front and back door require keys to lock or unlock. my children are small and would not be able to open a locked door.
The risk assessment here is clearly in favour of doors unlocked when people are in the house, so that's what we do.
Posties and deliveries have been known to one the door to pop something in. I'm ok with that, though was startled the first time it happened and talked to the postie about it. He did it because he knew I was disabled and struggled to get to the door, and I decided I was ok with that. Friends and family open, shout a greeting and come on in. Kids come and go to garden freely.
Yes, someone could take my car keys, iPad, purse, whatever in theory. In reality it's a negligible risk, involving possible financial loss, when compared to the risk being trapped in a house fire with doors locked, involving loss of life.
This thread has a lot of really disrespectful posts. Clearly there's are different ways to manage your door locking, but negligent vs paranoid is not how it is.