With the knowledge that death exists, more people will focus on staying alive instead of stunts and tricks that could kill them. If you didn't know that death existed, imagine how many choices you would have made that would have been life threatening. Knowing death exists, how many times would you have steered clear of jumping from that rooftop to the next, or other times that equally dangerous situations would have been avoided.
If you are aware of the Butterfly Effect, it states that the smallest things can create an even bigger catastrophe. Death is inevitable and finding a way to halt this will just go back to you in a worse situation. The Universe will always find a way to bring death back to you.