Uniqueness is what differs mankind from other creatures...
Each one of us is different physically, morally, mentally... We are biologically born different and individually special.
I think it's far too easy to judge, when meeting someone new, and, whether intended or not, a first impression sticks in the mind. And maybe that changes over the time if that person becomes a friend or if we get to know him or her better. But when someone falls into a certain category or group, people may directly link him to any other person that they happen to know or meet or already have any information about and they attribute him with a certain lifestyle, behavior or characteristics that may or may not reflect his reality but are mainstreamly associated with that group that he belongs to.
People tend to forget his uniqueness which in many ways makes him different from other individuals who also fall in the same category as him. A difference in the way of thinking or behaving that defines our human nature.
When you mention gayness in front of someone the first thing that comes to his mind is femininity, flamboyance and exaggerated hands movements ... His brain is programed to think that all gay guys are into fashion, love lady Gaga and Madonna, have tidy and neat rooms, and are the main cause of HIV spread ... Not to mention the infamous stereotype of gay men liking or wanting to have sex with anyone who has a penis. They literally dehumanize the gay just because he is gay. They forget the diversity aspect of humanity, they forget that people have feelings! This is what really offends when you stereotype someone, the fact that his identity is forgotten, that he will be stripped from his feelings, treated as an object not as a human ...
Maya Angelou said once that "Prejudice is a burden that confuses the past, threatens the future and renders the present inaccessible."
It might be true that the lack of proper education about certain topics is the main cause of stereotyping but the more dangerous is the refusal of any information that may correct a lot of ideas and prejudgements that people make. The majority of our society is still unwilling to do any research or at least read any article related to homosexuality or even discuss it in public! We brag about being a know-it-all but in fact we know nothing, a lot of topics are still blur to us and we refuse to clarify them.
People should open their brains before opening their mouths, in other words, learn about the topic before jumping into conclusions and/or uttering repellent stereotypes and prejudices.