On which issues should "both sides" be taught and why?

Is there another "side" to the cell theory, germ theory and the theory of gravity? We know that germs are not the only causes of diseases. In school, my high school teacher took about 2 minutes and dealt with the other "side", i.e. creationism. There is simply no evidence in support of creationism, so all he had to do was to tell us that some people claimed that life and the universe were created by some supernatural being and moved on. As for the holocaust, social scientists have researched the motivations of the Nazi Germans to see why they engaged in such horrendous acts. The "other side" therefore has had ample opportunity to make themselves known.