However, we probably should withhold paying obviously unsustainable pensions to current generation of retired citizens.

There's this desperate feeling that despite paying a large chunk of money into pension fund, my generation won't get any pensions at all, because of population ageing there just won't be any money for that. But brace yourself. And have a nice mood. (c)

We're just giving those money to aged people without hopes of getting anything back.

And no, immigration won't solve this, because every immigrant you bring today will retire (or try to), too.