I hate this mythical "good old days" B.S. I know people who live in the country who don't lock their doors because they live in the country. The idea that people who lived in urban areas ever could leave their doors unlocked is absurd.
This isn't what people mean when they say they don't lock their doors. I grew up in the country in northeast Ohio. I knew many people who simply never locked their doors, including overnight or even when they weren't home.
I live in Brooklyn now. Things are a little different here. My door has a $350 deadbolt lock that -- when it broke and locked me in -- took a locksmith, a serious drill and a couple hardened bits to defeat.
Whether you should lock something and how secure you make it isn't a binary decision - it depends on the value of the thing you're protecting and the likelihood of an attack.
I bet you would feel differently if you moved into the city or south of town.
Our garage leads to my office, which in turn leads to the rest of the house.
We came home shocked to see it open, and even more shocked that not a single thing was missing.