Your example of King Jong Un doesn’t work either, because it’s still a dictatorship, and father and grandfather were both dictators, and they both died, so why does it matter?
The world is overflowing with detritus because the incentive structures are not there. If people lived much longer they might be more willing to spend the time to clean up.
Supreme court justices serve for life. The only way to "oust" a supreme court justice (in the U.S.) is through impeachment. In the entire history of the U.S. no supreme court justice has ever been removed against their will. The assumption of mortality is deeply embedded into the U.S. Constitution. (Yes, you could amend the Constitution. Good luck with that.)
> so why does it matter?
Because there is at least a possibility that the next generation Kim might be better. Or that a Kim might die childless.
> If people lived much longer they might be more willing to spend the time to clean up.
Yes, that's possible, but much more likely those in power would continue to do what they do now: build enclaves for themselves that keep out the riff-raff.
If we eventually become a post-scarcity, multi-plantary species then significant life extension or immortality might work. But in the near future it would be a environmental and social calamity.
Yes, you should. Either that, or no one can have children. It's finite planet, and it's already over-flowing with people and their detritus.
Not only that, but if people don't die, then the first generation that doesn't die will end up ruling forever over everyone who has the misfortune of being born later. In a world where no one dies, someone like Vladimir Putin or Kim Jong Un can and will rule quite literally forever. The U.S. Supreme Court will have no turnover.