The boundaries are key here. You just found a community without thieves and our physical world has natural boundaries which prevent other people to enter your community. An analog is some kind of LAN with trusted peers. There's often little to no security in such a networks, the only security is firewall preventing any connections from the outside. But Internet is requires a completely different thinking. You are always living in the worst nightmare, everyone's attacking you constantly, checking your doors and locks. And there are such places in the Earth.

In my city you can't use a wooden door, because thief can easily break it with good kick, so everyone uses heavy iron doors with good locks. You can't leave your automobile with factory locks, it'll be stolen, sooner or later. Everyone uses additional security systems. You can't even leave your bag in the closed car, if your windows are not tinted. Someone will see it, break window and stole your bag. You must use heavily tinted window, so no one from the street could see anything inside. Even the thought that I could leave my car or home unlocked is foreign for me. It's my property, so it's my work to defend it.