Basically, the whole point is that the thing mirrors wage working in America.

So I'm wrong because the whole film is a metaphor?

If every child born in America is automatically given the procedure before birth then there is no choice in participating in the system.

So? Those people would still protest, riot and non-conform if they knew there was a better way for their children and for others in the future.

It's not like people only take political action strictly out of self-interest.

In extremely oppressive countries people protest with deadly consequences so others can live a free and happy life literally constantly.

And leaving it, while possible, is no more likely that people just leaving the ghetto in our world.

What? Immigration. You're thinking way too small here.

People leave Mexico because it's significantly less safe for them and they have significantly less opportunity than in America. And this is despite the fact that the risks are enormous and the chance of success is low.

Why not just keep money as money and only the rich are immortal?

This is a bigger plot hole though, you're right.

Although there might be an explanation for this... but I can't remember. I always thought they sort of 'harvested' the years from those lower in the social scale.

The 'sell' is "live like a 21 year old your entire life!" for the poor. And for the rich it is "live like a 21 year old forever".

The way they get a "net gain" in years is by, I assume, 'harvesting' them from those who are poorest. If they have a huge turn over because they're only living to 30-40 then you're 'gaining' 50 years per person.

This would explain why you can't just have the rich immortal because they need to get the time from somewhere.