^^^there have been incidences where animals appear to kill themselves, usually by starving themselves after someone/something close to them dies or dissapears (i dont think many of them comprehend the outcome of jumping off of a cliff or walking in front of a car or cutting their wrists and laying in a bath tub).
to your other point about animals not killing for sport, this is absolutely not true. ive read about tigers doing this, and not for food, but just going on killing sprees, lions kill the existing cubs after they take over, etc, but i will look more into it.
i think people have romanticized "animals" for various reasons, but have romanticized them nonetheless. murder, rape, suicide, no matter how much you want to pin them as human conditions are all observable in "nature".
i see your point that we seem to do things below what you would expect our intelligence to allow, but our brains are products of evolution too and there is still some primal shit in there, and there are people who want power and money and all that, mix that in with "society" and constant oppression and manipulation by more powerful people and its a little clearer,
i mean if you made a chimp wear a little suit and go to work everyday to a job he hated so he could take care of his whiny ass chimp babies and maybe his chimp wife aint lookin as good as when they first got married, her cooking sucks lately, mother in law chimp always tellin him what a piece of shit he was, he probably would cap himself, or atleast smoke to smooth out (oh yeah, there are plenty of monkeys in captivity addicted to cigarettes)