YANBU at all!!!
The killing of this stag was for PLEASURE. Not, herd-control, environmental protection, blah, blah, blah - it was because some weirdo enjoys killing beautiful animals. 
As Douglas Batchelor, Chief Exec of the League Against Cruel Sports said: "The Emperor had clearly become a trophy for bloodsports fanatics, and the inevitable price on his head was too great. His felling, especially during the rutting season, shows a shocking disregard for the vast majority of the British public who enjoy seeing these beautiful, majestic creatures in their natural habitat without pointing a gun at them."