I don't think it's fair to claim these people are all beginners. More likely it's a phenomenon where mature languages have been around long enough that you already know their strong and weak points, but when you look at a language in development you only see its potential.

I mean, it's not just true for new languages. For Haskell, you see beginners claim that "it's a perfect language and can do no wrong", while experts in the language will acknowledge its faults, including: long compile times, the downsides of laziness, etc.