I think it's dangerous to write off people who do stuff like that by saying they're "inhuman" or "insane." Humans have been killing innocent people in the name of hatred or religion since history began. To me that means it's entirely human to do it. That doesn't mean it is comprehensible. A great deal of what humans don't is incomprehensible, to me, anyway.
If I saw a shark eating someone I cared about, I would get very upset. The upset would take a lot of different forms. I might hate the shark, even though I know "rationally" that the shark is just doing its thing. I might be angry at the person for letting this happen to them, even though that might not make much sense either, they might not have had any way to avoid it. I might be angry at the government for not getting rid of sharks. I might be angry at the universe for creating itself in such a way that some beings have to eat other beings to survive. Or I might take a step away, take my upsetness and turn it against people who want to kill all the sharks. Or I might even take it in the direction of admiring the shark for being such a well honed hunting machine.
So far my expressions of such upset and anger aren't in the same league as those of people who fly jets into the WTC. But I think the differences are more in degree than in kind.
I've cheered action films where the bad guys get blown up. I've wanted people I thought were dangerous to get killed or punished or incapacitated.