But in general, if you don't want people to knock on your front door then put up a sign, or a fence, or some other indication that you want to be left alone. you'd better, because if you allow people to trespass on your land without doing anything about it - say they cross your land to go fish in a river that lies just beyond it - then they may develop a right from your failure to challenge them, sometimes known as adverse possession or an easement by prescription. And no matter how vigorously you defend your borders, you can't stop planes flying over unless they're going so low as to be hazardous to you.

Instead I will walk across everyone's property and if the police eventually stop me, I will say I intended to interview the homeowners but changed my mind.

I will occasionally walk up to people's doors and knock on them just to be plausible but since the law cannot read my mind or intent, they have to accept I am a journalist and have free speech rights to walk across anyone's property.

Obviously this is an absurd extreme example but it follows your basic rules. And shows why they fail. You cannot just walk across town, across everyone's property. Yet do it on a small scale to harass a single person and it is okay?

Instead I will walk across everyone's property and if the police eventually stop me, I will say I intended to interview the homeowners but changed my mind.

For example, this might come off as a plausible argument if you walked up a few houses and then turned away, but the plausibility of your argument diminishes in inverse proportion to the number of property lines you cross without acting upon your stated purpose. You seem to think that judges live in some sort of vacuum which renders them incapable of applying common-sense standards or their own experience to the facts of a case. Now, this is arguably the case in some civil law systems - Posner offers an amusing example of a French law which made it illegal to disembark from a stationary train carriage due to a drafting error - but it's a far cry from how our common law system works or has ever worked.

Yet do it on a small scale to harass a single person and it is okay?

Here you're doing something called begging the question - you're assuming your conclusion as a fact. You consider unwanted journalistic attention to an individual to be harassment, and so you ascribe that as a purpose to the journalist. Think about it; the journalist isn't going to someone's house to make their life miserable, but in pursuit of information, which information may (or may not) be an object of legitimate interest. Finding out whether someone is the architect of a multi-billion dollar digital economy seems like an entirely legitimate subject of journalistic inquiry to me.

I encourage you to post what happens when you do this and explain your theory here to a judge. Having seen what happens when somebody tries to outsmart a judge in his own courtroom, I promise it will be memorable.

In the UK, they sort of would. You can wander onto most private property until asked to leave, as long as you do not break anything. Only if you then refuse to leave is there any issue for a court or the police. Of course, if you just wander into someone's house and they attack you as an intruder, then you are not going to get much sympathy, however just the act of trespass is not inherently illegal. Other than in Scotland, where it gets a little more complex, on open ground I think trespass is criminal but defined as breaking camp, so walking around is still fine.