People want healthy

After watching how my cats reacted to one of their siblings upon return from surgery, I was a little surprised. Poor little Mario was drugged, dazed and confused as he stumbled around, trying in vain to keep his head and body in coercion. I was just trying to keep him from injuring himself as he searched around the back deck for some sanity. But Luigi saw him and was clearly displeased by his brother's behavior. It made him upset and when Mario got close to him, Luigi lashed out and tried to strike him.
What was the problem? Luigi sensed that something was wrong with Mario and he felt that this was threatening for some reason. Perhaps because Mario's health could potentially affect the other's health.

This is understandable and useful in survival tactics. Now let's extrapolate.
People are the same way (yes, heavy generalizations here). For instance, people are almost always put off by someone who is not cool. Someone who does and says things unfittingly, out of place--perhaps laughing too hard at their own jokes and talking way too much, cutting people off when they speak and being an all around goof. Generally, being uncool means that qualities have been identified which are beyond acceptable standards, and generally that is because a person initiates and carries thru on too many false pretenses. "I'm like, whatever, as if".
Specifically, dork says, "Wouldn't if be funny if I looked like you?" Er something.

Anyway, this ability to recognize people who seem out of wack can be a good thing. Specifically it can help you to identify who is going to be a problematic kind of person, one who has difficulties getting along with others in social settings, acting in contradiction to normal harmonic behaviors, unable to assimilate. It is useful to be able to do this, and that is why people instinctively react like this. When searching for a mate, a friend, these things should be considered.

However, it should also be considered that we should not act by instinct alone, for instinct can not guarantee happiness, only reproduction and life saving mechanisms among others. So, let's differentiate between the good and the bad, and quest for happiness baby.