Me quedó una cosa así:
I think that judging by appearances is something innate in humans but there are differences in the level of prejudice that we apply.
Some people love judging by appearances, although this doesn’t mean that they have a bad idea about the people they are judging. For example, you can see a slim man in his forties, wearing a dark suit with a patterned tie and having a drink in a coffee bar. You may think he should be a bank manager. You could be right or not, but in both cases, you aren’t doing anything bad. In fact, this is good exercise for your brain: to try to guess the jobs of the people you cross in the street.
In the other hand, there are some stereotypes that are absolutely wrong and can affect the relationships between people. Think in this: what are the people in the books or films like? Always, the ugly ones are stupid, malicious and coward and the good-looking ones are clever, generous and brave. We’ve been seeing this (in the fiction) all our lives so, when we meet somebody not very attractive, many of us think that he or she must be a bad and stupid person or similar: we usually lose the opportunity to know nice people because these stupid stereotypes.
So, what is my advice? Judging by appearance can be funny but don’t let your prejudice affect your real opinion.