Wiping out a species to save a single life is monstrous and absurd. I hope you're not serious.
The Green Party's original manifesto rejected this view; their position has some logical consistency, but I don't think that the continued existence of smallpox and rinderpest, or Guinea worms, or mosquitoes (http://www.nature.com/news/2010/100721/full/466432a.html), or Dutch elm disease (which doesn't really harm humans, but elm trees certainly suffer), is worth the suffering and premature death they cause.
So, I guess I could reduce my position to saying that if a species can only exist by causing harm or premature death to something more biologically complex than itself, it shouldn't exist. Do you think that this is reasonable?
I'd add two corollaries: that predation is natural enough that we shouldn't kill all predators; and that a species should only be wiped out if it has to cause this sort of harm in order to live -- if it's parasitic or infectious, or possibly (as with mosquitoes) if it's an extremely serious disease-carrier. And I'm not at all interested in driving mostly-harmless species to extinction for purely economic benefits...
While human life should be preserved whenever possible, there are situations where you must realize that human life is, from the perspective of our role as planetary stewards, cheap and disposable.
Sacrificing some lab animals, even thousands, to cure some obscure but crippling disease that affects a handful of people could be justified.
Wiping out an entire species to save a single person is atrocious, and completely insane.
If you're prepared to wipe out, say, otters to save one person then what's next? Elephants for another? What if it takes two or three species to save someone else. At what point do you stop?
Like would it be acceptable to kill all non-human life to save a single life? There must be some kind of line.
The "no consequence to humans" part is hugely subjective, but a case could be made that we're worse off than our ancestors because of how many species we've obliterated.
What I'm trying to say is (like the parents I believe) that the only thing affecting my judgement is humans qnd what the action does to them.
Shit happens, sometimes people die, and while it's unfortunate, it doesn't give us the license to turn one potential death into the extinction of an entire form of life.
Let's turn this around: What if some powerful alien life form had one of their citizens dying but they realized they could cure that individual by harvesting one planet worth of organisms. Given there's billions and billions of planets with life on them, what's the harm in killing Earth to save one of their own, right?