Do you not see politicians moonlighting as journalists in The Netherlands?
You see, there's a basic flaw in your thinking here.
If someone decides to be a plumber without appropriate training, they will either end up picking up no work or learn on the job and use their experience to become a better plumber and get work.
As far as I can see, Johnson has no training in journalism (and is not, correct me if I'm wrong, a member of the NUJ). So he says he is a journalist and becomes paid and is quite good at pleasing his readership ... he still gets work and it pays the bills. But that does not make him a journalist. He has no interest in reporting news or disseminating information ; or at least only in so much as it reinforces his (and his readership's) world view.
Your self-appointed plumber might learn the basics, Johnson gets paid despite not learning them and so has no motivation to learn them.
As I say, bit like Goebbels then.
On Edit :
Perhaps you are confusing journalism with copywriting.