And at least in England, trespassing is not even a criminal offense afaik, just a civil one - and the owner will have a hard time winning that case too, without very explicit signage.
Unless one helps himself to the house contents, or does other Bad Things, walking through unlocked dwellings will get you at most a slap on the wrist.
Outside of the cybersecurity analogy, as an American, that's . . . very disturbing.
Much like someone open carrying a gun is seen as potentially a few seconds away from committing a Very Bad Crime, so is someone walking around your house uninvited.
England has some weird (to me) property privacy laws. IIRC, you cannot be charged for simply walking through someone's property as a shortcut. There's nothing they can do about it, you just can't linger on the property. I mean, it seems fine, I just haven't seen anything like it before.
It's the system throwing a bone to the general populace in order to maintain an extremely unequal order. Aristocratic landowners mostly do what they want, and there has been no land reform for centuries, so a few concessions were thrown in to allow peasants to make a living somehow.
Well cutting across someone's yard != walking through their house. My friends and I growing up would sometimes cut through neighbors' backyards to go somewhere, and while we didn't have formal permission, no one cared because we knew each other.
I don't the know the situation now, but in the UK you could break into an empty place, then change the locks, and from that point on they could not evict you without a long process involving going to court. There was (is?) a huge squatters community because of this.
From the story of the GP, and extending your analogy, this is more like if they walked into the house and found the safe and noted it was locked, so looked up the safe schematics online.
Not exactly legal.
But even stepping back, I suspect walking around and jiggling random peoples’ doorknobs to see if they’re unlocked is probably illegal.
Unless one helps himself to the house contents, or does other Bad Things, walking through unlocked dwellings will get you at most a slap on the wrist.