Natural extinction

I've been thinking... while not the oldest by far, we're still a long-lived species, and inevitably we're going to see other species die in our time. While I definitely agree that we should try not to kill other species accidentally, I wonder if anyone considers whether we're saving species that were simply destined to die off?

Does anyone know about research into this? Comments in general?

I'd say that trying to prevent extinction of animals even when we are not involved with their low population in the first place (even though we almost always are) is the right thing to do, even if it is 'playing God'. I don't think anybody can come up with a reasonable argument towards us letting entire species die out when we have the ability to stop it from happening.