You can't be serious. Licenses for law and medicine impede freedom. They limit our choices of (and the cost of) legal and medical services. We are just willing to make this trade off because average people have a hard time determining the quality of these practitioners and we don't want people going to jail or dying in surgery because they aren't very smart consumers.

You can't "improve" speech without making it less free. Sometimes the loss of freedom is worth it (like yelling fire in a crowded room) but most of the time it is not worth it. Restrict our freedom of speech so that journalists can't use anonymous sources? Give me a break.

"I'll leave someone else to define [the standard]." That's convenient, since there is no standard that would be enforceable without being oppressive. I challenge you to come up with a standard that would solve the problem you state, that would be enforceable, that wouldn't be an insult to basic freedoms of speech. You also have to define what a "journalist" is. In the internet world, we are all journalists.