Staring at someone or something different is an instinct we have. Boils all over? Danger, stay clear. An unknown face? Someone from a rivaling tribe, danger. Irrational behaviour? Danger, could be rabies. Face deformity? Don't know what it is, possible danger.
You see, we didn't get this far by being polite and tolerant towards people that could put us in danger. Let's say your neighbour comes home from a trip to China. He's knocking on your door and you can hear him gasping for air, coughing and he mumbles something about borrowing some tylenol. Do you let him in, give him a hug and ask him to sit down and you'll get him some remedies? No, you stare at him through your window, conclude that his pale sweaty skin, his abnormal behaviour and funny breathing is dangerous to you and you call someone with a biohasard suit to take care of him. This is the very reason why we feel the need to stare.
Sheep stare a lot. They want to know what danger is surrounding them. I walk by sheep every day, and man those furballs stare at me intensely. Same with the local wildlife. And they don't seem ashamed of it either. And they shouldn't. Assessing your surroundings is wise. Assessing people around you is wise. So why is it such a rude thing to stare? Where did that idea come from? Today staring is synonymous with condemning, and that's a lie. Staring will in 99% of the cases lead to a person drawing the conclusion that all is good. No danger here. And we move on. So the next time you feel offended by someone staring at you, ask yourself: would I even be here if my ancestors didn't stare?
The answer is "no" btw....