People tend to get upset if you tell them they cannot have a particular item or piece of land because it would kill an endangered species or upset an ecosystem. This does not mean that these people do not care about the endangered species. Why we need biodiversity - the insurance policy. Monocultures may be easier to grow and harvest but they are more susceptible to being wiped out by disease. If we rely solely on one or two varieties of rice or corn we can quite easily find ourselves in a famine situation after some pestilence has destroyed the crop.
Natural ecosystems can be a buffer against other disasters as well.
Wetlands often absorb water that would otherwise cause major flood damage. If a wetland is not healthy it will not absorb water as efficiently. The problem is not that people will not agree to conserve a certain number of species, or the cute and cuddly species, but that it is hard to distinguish which species are absolutely necessary. Species which are vital to the survival of their environment are termed called Keystone species. When they are removed their ecosystem it falls apart.