"enhance those natural systems that benefit the widest number of people"
Right, excellent! It really is as easy as that. Someone buy that man a drink.
Now, how does one know, a priori, a) which natural systems those are and b) what they actually comprise? Here's an easy answer for you: one cannot. Natural systems are complex, to say the least, and we simply don't understand, therefore to act cautiously and seek to preserve rather than selectively ignore and hope for the best is the most sensible approach, surely?
That said, there's no reason why a pragmatic approach to ecology needs to be a punishment for humans, as so may extreme greenies seem to believe. I'm all for fracking and nuclear power, because the alternatives are so much worse, but I do feel very strongly that many current industrial and agricultural policies are going to cause significant long term damage. Sure, nature will carry on, because it has survived a snowball earth and massive volcanic eruptions and asteroid strikes and a few too many pesticides aren't going to kill it off right now. That doesn't mean it'll still be quite so useful to us all in a hundred years time.