Our entire social contract relies on the a redistribution of wealth from young to old. Boomer Communism, it's currently called.

If you are currently paying taxes, you are funding Medicare and Social Security (insert whatever name for your country). The deal is that when you retire, the next generation funds your entitlements.

If the next generation is not large enough, that deal breaks down, leading to almost impossible political choices. Do we increase taxes on the remaining working population to fund the larger retired one? Do we defund entitlements and tell retirees to figure it out, when they themselves paid into the system that is now bankrupt?