* The danger of overpopulation. If old people don't die, and young people keep making babies, our planet will become overcrowded soon. Which system should be implemented? A policy where you need permit by the government to have babies? Will we make a gigantic ponzi scheme where we put those extra humans on mars, then on other plantes, colonizing the galaxy? What when the whole galaxy is colonized? Intergalactic travel outside of our local group is quite hard, as expansion of space will make those galaxies leave us faster than light before we can get to them.
If overpopulation is really the biggest issue, why don't we just kill a lot of people? This isn't flamebait, I'm serious. If it truly is the worst possible problem, then let's just handle it, have a lottery or something.
I hear this all the time and it's so stupid. Nobody complains about overpopulation thanks to vaccines, cleaner water, cleaner/better food, etc, but start talking about keeping people from getting old suddenly it's a big deal. Do you think people in horrific places in the third world say "well, clean water would be nice, but then less children would die, and that would mean overpopulation!"
You can encourage birth control, you can send people to space eventually, you can encourage birth control, you can promote birth control, fucking birth control. And while we're at it, let's stop with this fantasy that children are a legacy as if we own vast farm land that need to be inherited.
And nobody is stopping a bus from hitting you, or a car accident, or anything else, it will catch up to you eventually, and hell as you even say without any irony at all:
* The danger of cancer. Often when rejuveniating cells you put them in a mode where they like to multiply. You artificially increase the likelihood for cancer with this to an extent of almost certainity.
As opposed to now where it's damn near certain as you get older anyway? If anything this helps your overpopulation problem, why the hell are you complaining!?