Simple; the reality of my "Existence" gives me the right to Survive using any and all means.
Here is a passage between Hump and Wolf Larsen from Jack London's The Sea-Wolf.
[Hump] “What do you believe, then?” I countered.
[Wolf Larsen] “I believe that life is a mess,” he answered promptly. “It is like yeast, a ferment, a thing that moves and may move for a minute, an hour, a year, or a hundred years, but that in the end will cease to move. The big eat the little that they may continue to move, the strong eat the weak that they may retain their strength. The lucky eat the most and move the longest, that is all. What do you make of those things?”
...
[Wolf Larsen] Again, what’s it all about? Why have I kept you here?—”
[Hump] “Because you are stronger,” I managed to blurt out.
“But why stronger?” he went on at once with his perpetual queries. “Because I am a bigger bit of the ferment than you? Don’t you see? Don’t you see?”
“But the hopelessness of it,” I protested.
“I agree with you,” he answered. “Then why move at all, since moving is living? Without moving and being part of the yeast there would be no hopelessness. But,—and there it is,—we want to live and move, though we have no reason to, because it happens that it is the nature of life to live and move, to want to live and move. If it were not for this, life would be dead. It is because of this life that is in you that you dream of your immortality. The life that is in you is alive and wants to go on being alive for ever. Bah! An eternity of piggishness!”