It may be possible to reverse aging. Doing so risks severe overpopulation.

Not sure why the title here complains about overpopulation when the title of the linked article doesn't contain the word.

If one truly believes that we should not try to extend anyone's lifespan due to overpopulation risks, that is equivalent to wanting people to die earlier than they have to, which is equivalent to not caring about attempting to treat aging-related illnesses such as cancer (the reason being that the best way to live longer is simply to lower the risks of what is most likely to kill you as much as possible, so neglecting this is equivalent to a shorter lifespan). I hope wanting people to die is not a very popular view and find it confusing how many people believe Earth is anywhere near its carrying capacity. Perhaps the main argument is related to environmental impact, but this obviously is not a static ratio of impact:person years, and is meanwhile improving in many areas.

While not a masterpiece, this book does a great job with the thought experiment of this: https://www.goodreads.com/book/show/10673576-the-postmortal

the same (lame) argument applies to any medical treatment