I assume you mean that dying is the most terrifying pat of the natural human experience. Also, I'm not sure why you infer that me thinking death is a natural part of life, means that I'm happy or eager to die.

There are many reasons that people living forever would be a problem for society, the most obvious being an ever-increasing population.

> the most obvious being an ever-increasing population

https://en.wikipedia.org/wiki/Thomas_Robert_Malthus