This is something I have given a lot of thought to.
I saw footage of a gazelle being hunted by a cheetah. My reflexive thought is -- how unimaginably horrible. Here is an animal which is evolved specifically to hunt you down and kill you. And every moment you spend trying to live is a moment lived in fear of this awful creature. What a life! My horror does not even compare to the horror of this life.
But, watching the gazelle slalom and jump with incredible precision and grace, there is another thought: that the gazelle was also born to run. It uses its God given abilities to the absolute maximum possible extent. During the chase, it is in a state of complete flow, more complete than any Olympic athlete could ever hope for. The sheer concentration required, the exertion, the split-second decision-making required to avoid getting caught. To master this state is to escape the predator, and it must feel incredible to outrun a cheetah. Incredible in a way that is impossible for a human living a modern lifestyle to fathom.
To fail means to die, of course, and that cannot feel good to a gazelle. But it's just death. We all die anyway. Human beings, gazelle, cheetahs. It is a simple fact that you will die.
So, then, whose life is better? The gazelle's, whose time is spent performing in the most integrated and pure way possible? Or the human's?
The human's life, which is spent doing activities its body was not designed for, in social situations his brain is not built for, eating things his stomach was not designed for? And then, we die. Just like the gazelle.
Interesting to think about for sure. I myself have no option — synthetic insulin keeps me alive.