Preservation of Biodiversity

Biodiversity: this is the sort of thing that people can accept on faith as a moral issue (more in the sense that it's the right thing to do than just "oh don't kill the polar bears and baby seals nooooo").  Looking at it as a practical issue, though, ignoring anything morally questionable about it, I'm actually a bit less convinced after researching it than I was before.  Don't get me wrong, biodiversity something worth preserving, but we haven't really put together a very compelling argument against saving it from, well, us.

• One common argument for preserving biodiversity is that there is potentially a great deal of medicines and other, similar benefits from species not yet studied, and if they went extinct we would lose that benefit forever.  This begs the question, though, why should we bother preserving biodiversity once we've identified and safeguarded the species' of value to us?  Once scientists have meticulously studied and gone through every plant and animal on the planet, this argument no longer holds much validity.
• One less common argument is that biodiversity can act as a safeguard against natural disasters: but usually when this is brought up it only refers to forestation and similar, which seems more like an argument against deforestation than anything, and that is different than biodiversity.  For example, why not just select the kind of tree best suited to defending the area and leave the others vulnerable to logging and natural hazards?
• As far as food sources go, with the progress of genetic engineering to create species more useful as food sources, we could preserve the backbone of a diverse diet while allowing other species to phase out at their leisure.  Sounds pretty cruel, but again, just an objective view.
• Finally, there's the obvious fact that people appreciate the aesthetics of biodiversity, but that's a pretty superficial cause to spend millions of dollars to preserve, and one that probably wouldn't drum up enough interest to, for example, save the rain forest (heh).

Yeah, I don't know.  I haven't seen any other major arguments than these, and it raises questions...

I don't have the prompt handy, but I'm pretty sure this addresses it well enough.  This is also pretty excessive for a post, so I guess I should cut it off here.  Bye for now.