What's the best way to refute social-science-type arguments for egalitarianism?

The 2009 book "The Spirit Level" argues that income inequality has a broad range of negative effects on society. "It claims that for each of eleven different health and social problems: physical health, mental health, drug abuse, education, imprisonment, obesity, social mobility, trust and community life, violence, teenage pregnancies, and child well-being, outcomes are significantly worse in more unequal rich countries." (Wikipedia: http://en.wikipedia.org/wiki/The_Spirit_Level:_Why_More_Equal_Societies_Almost_Always_Do_Better ) What's fundamentally wrong with these arguments? What's the best approach to refuting them? See also the TED talk by author Richard Wilkinson: http://www.ted.com/talks/richard_wilkinson.html