That's a nice way to restate that young people will have to produce more, and receive less. But tell me, what incentive do you have to produce more when you'll just have it snatched away to be given to someone else? Why not move to the U.S where your productivity will be rewarded, or just put in minimal effort?

Young workers will produce more regardless because people don't stop being innovative. The incentive to produce more is that economic surpluses improve the standard of living for everyone, including young workers.

Is it better that retirements are funded by this surplus from the increased productivity, or by direct taxation on the income of young workers? Income growth doesn't keep pace with productivity so it's an easy answer.

Taxing the income of current workers to directly fund current retirees is the real "snatching away what you produced". If more national pension plans invested in broad-based stock indexes instead they wouldn't need to take more and more money out of young people's pockets.

Capital ownership entitles you to its returns. Young workers typically don't own a lot of capital. So it comes down to either retirement plans owning it, which means young workers also get its returns when they retire. Or a small wealthy elite could own it all, and everyone else gets left out, reduced to moving a dollar from an youngsters pocket to a retiree.