The main problem being discussed here, as I see it, is a question of absolute vs. relative ethics. Should there be no killing of animals for sport, as we should try to be the best as we could be, or is it better to allow one to be hunted to potentially save others?
IMHO, this is a very similar argument to allocation of limited resources in, for example, health care. In Canada, about a third of our health care budget goes towards keeping people alive in their last three years of life. Could that money keep more people alive with a higher quality of life by spending it in less developed nations? Or on medical science? Absolutely! But are you going to be the one pulling the plug on your grandmother?
My 2c worth (rounding down to 0 since the penny is no more) is that there are far more critical issues, like people killing people, to spend our time and money on than, for example, to spend our time lobbying governments on this one way or the other. I don't live in the country where this is being done, I don't know how poor they are, how much help the other Rhinos need, or how much they are being hunted regardless of how protected they are, or if the money will help keep other Rhinos from being hunted. Let the people that live there that know all of the complexities make the decision.
I don't like the fact that this is being done, but I would feel a lot worse if I didn't recently pay to have a chicken kabob, or if a lot of my friends and relatives didn't hunt. I would agree a lot more with Draugnar once we are a little further ethically forward with our treatment of our own species and better ethically manage resource management.
As for other species not looking out for other species, there are lots of examples of dolphins saving people. I talked to someone decades ago who was pushed back to safety by some dolphins. Black rhinos, not so much, but there are community-minded animals out there that recognize and help other species without gain to themselves.