I have a lot of experience working with animals both wild and domestic. I've hunted and killed lots of wild animals in my life, and I've slaughtered lots of domesticated animals too, in most cases for food. I've killed animals in self-defense and in defense of other prey animals. I've also done a fair amount of what I consider to be mercy killing of animals. An animal who's outlived its useful life or is suffering deserves, from my human perspective, to rest and to meet that rest with as little suffering as possible. I do not hunt for trophies or sport. For me killing is about food or mercy, and in some cases defense.
Killing is not usually a pretty thing. For anyone who's not used to it, it can be nauseating to think of. I doubt the hunter in this case intended for the animal (Cecil the lion) to suffer for nearly two days before he dispatched it, but that sometimes happens. I don't see anyone throwing rocks at the American Indians' historical practice of taking large animals with bow and arrow, and some of those animals took weeks to die. That said, illegal killing is despicable and should be dealt with accordingly. I don't know who broke the law in this instance, if anyone did. But if someone did break the law then they should suffer the consequence.
When it comes to hunting for sport, ironically in nature I find the cat family to be notorious at killing for the sport. I see it all the time, even among domesticated cats I see it. Often I've seen cats prey on and capture animals to do nothing but kick the critter around until it ultimately is dispatched. Not to humanize it, but from a human perspective it looks like entertainment. Nature is brutal.