Why does Kennedy repeatedly refer to "both sides" in the middle of the speech? What i=effect might this repetition have on listeners, including those on the other "side"?

1. To appeal to other countries that might be at war or foes of the United States of America. So, the United States and the other countries are the both sides.

2. The effect of this on the audience including those on the other side would be a softened emotion that would prompt them to strive for unity.

Explanation:

President John F. Kennedy on his inaugural day delivered a lecture to the American audience which was broadcast worldwide. In the middle of the speech, he started several sentences with the phrase, "Let both sides...". By referring to both sides, he was making reference to countries that were in opposition to the United States. He implored that they seek peaceful ways to resolve their problems instead of resorting to violence and the use of arms which were negative inventions of science.

This would have appealed to the emotions of his immediate and extended audience, helping them realize that war was not the best option for them. They would also come to see civility as a better way to deal with their issues.