Yeah, I watch Vice too. They have some interesting stories, but then, that's the goal of the hipster-cum-SMEs. Not everything on their show should be taken as a full picture of reality, let alone retold as gospel without citation in a Slashdot post.
In some amazing leaps of logic, the [NSFW] "documentary" cites low birth rates and then, taking this to be self-evidently a problem, finds a couple of people who say they're basically afraid of women, and then goes on to paint an entire culture in broad strokes. But here's the thing: Industrialized nations have the lowest birth rates in the world, so one might as well conclude else that Japan is the most advanced nation on earth, which is a distinct possibility. Indeed, overpopulation is perhaps best viewed as a problem, not a goal.
I'm hardly a Japanese fanboi. I lived there for six months, for work, and I wouldn't go back if I had the choice. There's some stuff there that certainly seems weird by western standards, but I didn't see any indication that it's a culture in decline. Their GDP growth rate might not be off the charts, but that's hardly the most important indicator. India, for example, has both an amazing GDP growth rate AND population growth rate. If you want to know what it's like to live there, well, there's another Vice story about that.