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
Fertility rates are below replacement, which means that population sizes are convergent. A decreasing population is a more likely future scenario for many western countries, even if human lifespan was indefinite.