One argument is that death and limited lifespans are advantageous for the species overall. More sex, gene mixing and having offspring is better and allows for faster adaptations.

Plus ideas can change faster as culture changes.

That said, there may be ways to overcome this and I still think it's worth working on not having to die. Though trying to determine purpose behind existential questions becomes difficult pretty quickly.

Even if we figure it out since sex and having children is core to biological life and the basis for the replicating genetic code that eventually lead to us - not sure how we'd solve that. Guess we also better get working on space colonization for our start trek future.