This is an interesting quote from the article given by another biologist Stefano Piraino, not the main focus of the article. If we did find the secret to immortality, it would be stupid to give it to everyone. In that case, who gets it?
Will it lead to overpopulation? Yes. Bloody wars? Yes. Almost completely stagnant population? Suicides left and right by 200-y.o. people? Perverse class imbalance? Complete overhaul of society as we know it? Yesyesyesnotreally.
Because once you institutionalise and put such and such rules in place (a bureaucracy), people stop thinking. They stop thinking and become not people, but things - and they do it to themselves, willingly.
And that is the greatest crime of all.
As far as the "immortality" for these jellyfish go though, they are rather easy to kill. They can't even eat a whole prawn egg, and their water temperature has to be just right.
And you can't adopt nor rent a womb.
There, no overpopulation problem.
Also, if humans do go extra/multiplanetary, most religious apocalypse' are MOOT.
It might potentially be fair to administer "longevity" to those willing to colonize another planet. This would solve the problem of distribution while creating a bit of an incentive to expand human civilization (which might well be an eventual necessity).