>> I also pose this as a completely honest question, as I don't really know if you wiped out every desert ecosystem with solar/desal/etc if it'd actually affect anything else.

Presumably, you believe that there is something amongst all that "anything else" that has intrinsic importance. Perhaps for you it is humanity in general. Perhaps just yourself and your own family.

Whatever something you might value intrinsically is fundamentally arbitrary. Why not me and my family? Why not other great apes besides humans?

Arbitrarily, I value (desert) ecosystems as having value in their own right. Biodiversity is an intrinsic good, with no further justification required.