Why do Americans love JF Kennedy so much?

I have heard people talking about how American he was. Embracing freedom, human rights and equality. But according to what I have read about him, he supported dictator Diem, during the Vietnam War. And that is like the complete opposite of what America stands for. He was against NLF, who wanted more freedom and better human rights in Vietnam. Was it only because Russia supported NLF, America was against it?