If you agree with the evolution idea that human was evolved from the ape, it makes sense that we are the result of a genetic mutation process from the monkeys. And as biologically proven that any sort of genetic mutation species is self destructive, then our self eliminating behavior is understood. By rule of nature, there is no need for intelligence, so perhaps that is the reason that all the intelligent civilization in the history have been extincted and the less intelligent one survived. Naturally, intelligence is not needed for survival of the gene. Instinct is enough, as it is proven by the fact that monkeys have survived so far with out intelligence. So if you agree with the theory that evolution of intelligence was just a accidental genetic mutation, it is easy to accept all of the self destructive behavior created by it, such as love, greed, sacrifice, addiction, suicide ...

Another good example of self destructive behavior being a result of genetic mutation is left handed people. The reason there are more right handed people, is because that is a more life sustaining choice for survival. Being left handed is another degree of mutation, which causes left handed people have more tendency to self destructive behavior.

One self destructive side effect of intelligence is boredom. That is a concept that animals dont experience, therefore live a happy life, whether they have food, and mate, and other survival necessities. But human suffers from boredom, which is not a natural need, therefore we do thing to satisfy it by doing things that are not good for our natural need which is survival. I believe the source of all evils and stupidities in human life is boredom,