I'm not supporting this idea because I think it would discriminate newbies. Many of them came to forum only to contact forum members when they need to solve some issues, get answers to their questions and PM's sometimes can be only way to do it. I can say that I received lot of messages from newbied and I didn't found any attempts to scam or do some other bad activity. I would agree with OP idea if these phishing would be massive problem, but now I think forum have more serious problems to solve.
If a newbie does have a question he would like answered, a post in Beginners & Help would be the appropriate.
You don't need to have access to PMs to get your questions answered.
That's the point, they need to be "discriminated against", because they cause the most issues from throwaway accounts. As mentioned, newbies can start threads or cry in their beers when they have problems. I think this is a swell idea. Would be nice to see some action rather than endless debate.
Newbies often came to forum when they have issues with exchanges, gambling websites and other services. Offcourse, they can start thread about it, but there will be no guarantee that someone from service staff will respond to the thread.
And I don't think that forum administration will restrict newbies from sending PM's because in general they don't fight against scammers. They can declare that they are fighting aginst scammers, but how they do that - forum even have dedicated place for scammers, called "Investor based games", where they have absolute freedom to promote their scam services.