A more interesting argument against doing this is considering the tradeoffs if implemented:
* e.g. the AMA has pretty successfully restricted the supply of doctors and driven the prices of medicine up,
* people are so paranoid about giving medical or legal advice they have to say things like "I'm not a doctor but... I'm not a lawyer but..."
etc.
In the case of doctors, pharmacists and lawyers,things like surgery, controlled drugs, rights of audience are easy to restrict. If you are not one and try to do the job anyway, you won't get very far.
As a client, I cannot use a partitioner who is not licensed in my jurisdiction. If I have a video consultation with a real foreign doctor, they still can't write me a prescription I can take to my local pharmacist. No matter how good the doctor is, they are made deficient by not being registered with the GMC.
A journalist writes and publishes articles about current affairs. You can't legally prevent people doing that without a catastrophic infringement of free speech.
Every day, I read articles from publications from many countries. Those articles are not made deficient by the fact that they are not written by NUJ members.
Plenty of people read and believe bunkum written by people who don't even pretend to be journalists. Sticking little "licenced by..." Logo on the real stuff won't make a difference there.
How do you prevent independent journalists selling pieces to certain outlets without unfairly placing the burden on the journalist? Is it a list of proscribed publications? How does a publication get on the list? What happens to all the "good" journalists who work for an organisation when it gets put on the list?
What, exactly, is a journalist? Does it include columnists who write opinion pieces? If not, how do you prevent an outlet from running more and more "opinion pieces" masquerading as news? If you get defrocked for doing something your employer considers highly profitable, they can just rebrand you as a columnist.
What does it mean to be licensed? What does having a licence allow you to do that you can't do without one? Is this your "press pass" allowing you to ask questions at briefings? There have been cases recently when this has been revoked on a whim. Is it just to get a byline in a printed newspaper? Again, they can rebrand unlicensed journalists as runners, and print the piece under the name of a real journalist.
Journalism is not a terminal career like medicine or law. If you get thrown out of one of those professions, you lose your livelihood. There is nothing else that you are as well trained for that pays as well. You have to start at the bottom of something else. Most journalists are not particularly well paid. Former journalists can earn as much, if not more, writing press releases and advertising copy.