Animals don't deserve to become extinct? What justification? Who's to say if an animal has an inherent right or deserves to be treated on way or the other. Creatures do not deserve anything inherently, the natural order only affords physical and mental attributes to a species, if not afforded certain characteristics and your species is prone to extinction, it will go extinct, other species will prevail. The cognizance, or lack thereof, of the intentions behind one's own suffering does not make an act of predation wrong inherently.
Mere existence of other animals does not in itself cause detriment to society, true, but the mere protection of animals in certain cases is a detriment to the thriving existence of humans. You have taken five words from my post and put them into a completely different context.
For instance, medical research is most efficient with animal testing. Certainly, protecting animals from animal research would hinder the research process of medical advancement and therefore cause loss of human lives if animal testing were otherwise employed. That is just one, of many reason as to why leaving animals alone can be a detriment to society.
It does not matter what the animal's will is, animals have a will to not die, that sometimes does not coalesce with human interests to thrive. Advocacy against the mere suffering and pain along is albeit without a substantive purpose that is not logically based on the betterment of human society. Acting against one's species or society, again is a breach of duty to natural order, ultimately causing pain/suffering to one's own species rather than other species.