Why Do We Always Assume Things?

Ever jump to conclusions about someone or something? Sterotypes, maybe? You know what they say when you assume things, right. So why do we?
Like if two teenagers go into the planned parenthood, we assume two things: they either are having a baby, or having sex. They could be going there with a friend, or for a friend, or just plain old asking questions about the matter of sex and STDs.
Or two people, boy and girl, were friends. People often assume that you're dating but you're just friends. But thanks to that word, assume, people jump to conclusions all too quickly.
Or a boy with long hair, and straightens it. We assume that he is either gay, or just strange, when really he could just like his hair like that.
So why do we assume things?
I think that assumptions are something we as human beings can not help. I think that we come up with judgements, as a way to shield us, as a way to protect us from all of those who scare us. Coming up with judgements is something that protects us about things that we are afraid of facing because its something different than what we are used to. Being different is scary, because all of them haters are all up on you trying to bring you down. I think if you chose not to be labelled, then you are considered wierd. Everyone tries to give you a label, whether it's a handbag, or on what kind of person? Why must we type someone or something? Isn't the quality of it good enough?
Well, if you assume things, you make an ass out of you and me, so why do we as a society come to make an ass out of ourselves, whether it's family matters or a celebraty? Why do we have to type someone, or something? Isn't our time better spent getting to know them first?