A) Retirement creates a better equilibrium, for the economy as a whole. Not just because you flush all the people who have lost a step and yet have enough social/economic power to hide it out of making decisions, but because it clears the way for ambitious younger people who are getting blocked out of advancement opportunities because the generation ahead of them just isn't #%@#$ leaving. Not that I have any experience with that, obviously. You can have a equilibrium where everyone works until they physically can't any more, but that's simply a worse one, for almost everyone.
B) If we're going to have retirement, it is a better equilibrium for our economy as a whole to do it through some sort of enforced group savings plans rather than individuals. The big risk with retirement is outliving your money. If you have a group of a hundred thousand people, you can statistically infer that X% of them will be dead at age 75, and X+Y% of them will be dead at age 76, etc. (1) So you don't need to save as if everyone is going to live to be 90, only some percentage of them. But if retirement is entirely individual responsibility, then everyone needs to save as if they are going to be 90, which leads to an unnaturally high savings rate and that leads to weaker current economies (2) and giant pools of money seeking high returns(3).
1: Yes, improved medicine might change the exact distribution here, but that is projectable, with a small fudge factor you can basically ignore it.
2: That money is saved, not getting spent and turning into your neighbors income!
3: This is what caused all of those boom/bust cycles in our economy over the past 20 years.