I will not argue that. First impressions are vital, and if you don't think so, take a walk down a dark alley at night and talk to anyone you meet with your wallet in your hand. And of course there are exceptions to generalizing. I think my point would be stronger in an earlier time period when everyone had predefined roles in society and there were few variations. Everyone else was just labeled as 'heretics' or 'witches'.
People apply to their categories even less now that they are exposed to different ways of life.
Emphasis for generalization will rely less on looks and more on economic status. In short, it signals that we are turning into one global commercial culture. All generalizations are false, including this one. Ben wrote, bitterly. We generalize all the time.