Earlier quoted context omitted.
Should companies also require their employees not be overweight because they are less likely to miss work due to illness?
Or to be sterilised so they can't get pregnant or make their partner pregnant. Having kids leads to missing work after all.
In general, when an employment discrimination is not specifically forbidden via the Civil Rights Act (or interpreted as equivalent to something explicitly forbidden by the Court), it is legal to discriminate based on it in the United States. Beyond that, the Court and the legislature are (from a political philosophy standpoint) generally willing to let individual employees and employers (or employers and unions) hash out the messy details.