They are allowed, but they shouldn't be, because there isn't an objective way to judge what is a beginner question, and what is not. And when a beginner question isn't the right fit for Stack Overflow, there isn't an objective criteria to explain why.
From the FAQ, Stack Overflow is a site for Programming Professionals and Programming Enthusiasts. I believe that this makes it hard for us (pro's and enthusiasts) to empathize with new members and beginner questions.
What is the bar for research effort? It's subjective, and so can't fairly be applied, so instead, just flat out ban beginner questions because they have no relevance to SO.
I think what's more true for every new beginner question, there's likely an applicable duplicate already in the system. So do we prevent beginner questions? No. Do we aggressively close them as duplicates when found? Absolutely. And downvote for poor research.
The problem with this approach is that "poor research" is subjective. Along with closing dupes, and downvoting poor quality questions, I believe we should educate beginners to Stack Overflow. It's very obvious when the dupe shows up, as well as a Google search of the same question returning multiple sources with the solution, to point out they should first attempt to google, or search the site.
But what about when that's not the case? Googling that question doesn't return good results, so at least by the Google test, it was fine. Also, it wasn't closed as a dupe. Instead it was downvoted as a beginner question, for lack of research. The comments (since deleted by a mod) to the OP suggested she should try to have an attitude of learning before asking a question. As a Quote above in a previous answer suggests--that she was an idiot for not doing research.
The problem with allowing beginners is that there isn't a positive way to help them be successful. A deluge of downvotes, comments akin to "RTFM", and closed questions isn't welcoming, and is counter to the spirit of which I believe SO was built.
For what it's worth, I believe beginners should be allowed, and new people to our site should be given a chance to learn how to better use our community. As it stands, we don't have a way to do that.