O.P. States that the Rhino was shot legally. My understanding is that hunter tags are sold for older endangered species, and the money from that paid tag pays for the wildlife protection agents to protect the younger/healthier members of the species.
The creation of this market incentive allows the Rhinos to exist into the future. Without a market incentive, no agents would protect them, and starving people will hunt them to extinction.
I'm open to being wrong about this, but this is my understanding and it makes logical sense to me.
That being said, fuck anyone who celebrates a death in this disrespectful way.