Discrimination Based on Appearance

Contingent Workforce recently cited an article which appeared in the Indianapolis Star which noted that 40% of Americans in a recent poll indicated that employers should be allowed to discriminate based upon appearance.  Appearance included such things as weight, clothing, piercing, body art and hairstyle.  The survey also noted that 47% of those with supervisory responsibility agreed that discrimination based on appearance should be permitted.

The problem here is that if we let people exclude people from employment based upon their appearance, at what point have gone too far into the gray and it becomes unlawful discrimination?  Do certain "groups" of people wear a certain style of clothing or dress?  Do people of certain religious backgrounds wear certain displays of their faith?  Just how fat (or not so fat) do you have to be to be considered just "overweight" and subject to lawful discrimination?  What about people who just aren't good looking?  Should we hire only tall thin blonds?  I thought that good people practices involved hiring based upon qualifications and experience.