Examples abound. Here are two:
Absurdity #1: Pure human races exist.
A resulting atrocity: the Holocaust (~20 million people, including ~6 million Jews, killed by the Nazis in the 1930s and 1940s).
Absurdity #2: Acts which are both suicidal and homicidal can be wonderful things, and can earn a person an eternal reward in paradise after death.
A resulting atrocity: the destruction of the World Trade Center, and attacks on other targets, on September 11, 2001, which killed over three thousand people, including the hijackers themselves.
Please note that this list is far from complete. A complete list would fill several very large books. Beware of absurdities in your thinking, for they can actually be fatal.