According to dictionary.com, a meaning of "assert" is to defend or maintain. That being so, the History of mankind is replete with assertations against Nature (animate and inanimate) of man's right to live.
"What right to life does a man drowning in the ocean have? The ocean will not hearken to his cries."
Stupidity is often a Capital Crime in nature, so it sort of depends on how he came to be drowning, but that aside, he has the same right to life he would have if he was not drowning. It does not matter if the ocean does not hear him. A potential rescuer might. Or he could swim.
Let's rephrase that: "What right to life does a man attacked by a lion have? The lion will not hearken to his cries." The answer is much the same as what I said above. If he has no right merely because he's attacked, he is only prey.