There is only a finite number of living beings this planet can sustain at any given moment - if there really is a possibility to "disable" aging, how do you think we should decide which of all those potential beings will be given a chance to live? Who are we to consider ourselves more worthy of life than any of the previous or possible next generations?
"on this planet." Maybe that would give people motivation to get off it. Regardless if you want to weigh counter-factual people against living people your moral system will have some curious implications which you might not like. If someone threatens to not have children if you don't give them your money are you going to take into account the non existent future lives snuffed out and give in?
