Many people greet evidence of biologically based race and sex differences with extreme skepticism, even hostility. We argue that some of the vehemence with which many intellectuals in the West resist claims about group differences is rooted in the tacit assumption that accepting evidence for group differences in socially valued traits would undermine our reasons to treat people with respect. We call this theegalitarian fallacy. We first explain the fallacy and then give evidence that self-described liberals in the United States (...) are especially likely to commit it when they reason about topics like race and sex. We then argue that people should not be as worried as they often are about research that finds psychological differences between men and women, or between people of different racial or ethnic groups. We conclude that if moral equality is believed to rest on biological identity, ethnically diverse societies are in trouble. (shrink)