You may call it envy if that's how you see it -- if you indeed are interesting in learning about the many problems of economic inequality, I recommend the book The Spirit Level (http://www.equalitytrust.org.uk/resource/the-spirit-level).
I can think of no mechanism besides envy which would cause income inequality to harm anyone. It's not as if the US poor lack some good or service which is available in other, more equal societies.
Note that the Spirit Level only provides a correlation between inequality and other problems. It does not show the direction of causality.