>Yes, a person votes in his own self interest - that’s how that works

No, that's not how that works, some Rousseau might be in order. What early Republicans still recognized is the concept of General Will. That a polity is not just the sum of its individual interests but requires an orientation of each member towards the shared common good. A democracy that is governed by self interest, in which simply put each vote is bought is a democracy in decayed state.

That this doesn't even register with people any more and is perceived as the norm is exactly what I'm talking about when I'm saying that most current democratic nations are at the end of their life. If young people are a demographic minority and each person votes only in their selfish interest the future of the nation is, by definition, dead.That they opt out in that situation is actually rational.