Nazis thought that killing jews, gypsies, and other groups would only make those groups stronger. purify the german race. make germany a safer place. prevent future wars.

Naturally, the answers would be: Purify the German race, make Germany a safer place, and prevent future wars, but since there is only one answer

The answer would be Nazis thought that killing Jews, Gypsies, and other groups will purify the German race, since the Nazis basically accepted people with "blond hair blue eyes", they were trying to purify a master race, called "Aryans".