I think you are understating the extent to which mailboxes and homes are secured by men with guns. Sure; there’s very little preventing someone from kicking their way into someone’s house, but if someone did so, they would very likely end up in a jail cell or even, in some places, dead.
Unfortunately, you can’t physically harm people over the internet, so different security measures must be taken.
Your odds are very good stealing from my mailbox and not that bad burglarizing my house. Maybe you have much more vigilant police where you live. What’s more, unauthorized access to computer systems is also a crime.
The odds of getting caught robbing a single mailbox are not high, but if you do it on a large scale, it starts to get pretty risky.
The odds of getting caught attacking a Russian computer from the US or attacking a US computer from Russia are essentially zero for any scale small enough to not have major foreign policy implications.
Homes are massively protected by people’s goodwill, not by the judicial system. In most of Europe and more than you suspect in US too, if you call the police, they come more than 30 minutes later (especially in France where they have no right to use their guns and don’t risk their own security), and if you “handle the matter yourself”, you are in just as much problems as the thieve, particularly in US where you still have to use a lawyer to prove your innocence. No, what really holds houses from being broken into, is mostly that people don’t do it (hence the use of a society where people earn enough to not be willing to risk physical fight).
Most forms of security rely on the goodwill of most people in society; the entire problem consists of handling the minority of people who lack goodwill. These people exist in every society.
Unfortunately, you can’t physically harm people over the internet, so different security measures must be taken.