Re: "enhance those natural systems that benefit the widest number of people"
Spot on. No (sensible) person thinks that nature is going to 'die', although it is beyond doubt that humanity is capable of (and has had great success at) 'weakening it' by reducing biodiversity.
It is however quite plausible that we could alter it sufficiently to cause ourselves as a high-in-the-food-chain species major problems.
And that's assuming you don't consider the loss of species at a shocking rate as an innately bad thing - whereas I suspect that most people do consider this bad, and would rather not have to explain to their grandchildren why there are no more tigers, whales or bees.
Sure we may be able to survive in an ecosystem without tigers, whales or bees. But if we can avoid it, surely it's better not to find out.