Culling deer / grouse is not the same as wiping out rhinos. It's fine to hate the royals, but there are better reasons than William's attempts to protect endangered species.
Tell that to the deer / grouse.
That's like saying if you manage a garden and like flowers you're not allowed to cut the grass.
No it's not. It's like saying if you manage a garden and like flowers you probably shouldn't destroy someone else's garden and flowers.
There are many reasons to hate the royals, this is another one of them. Being a professional philanthropist on the tax payers pound and ill-gotten wealth does not make you a good person.