It's just how you were raised, the way you grew up, and the environment you lived in that determines that thing really. It's all about how strongly your family feels about something that you 9 out of 10 times adapt their way of thinking and respond with the same feelings. You'd have to really live in a very open environment to not feel nit picky over the tiniest things like one's skin color, the color of their hair, the nationality, their religious belief, their gender, ect.
Some people get the privilege to live in a freer life style where they end up accepting anything and everything no matter what the box of life they see and even the contents of said box. I've been lucky enough to have been raised with an open mind due to how badly my mother was raised, she made it possible for me to see that comforting side of the box and keep my arms open towards my friends who like the same sex or choose to become transgendered. It's just the way you are brought up and the environment you live within that can shape your world, ideals, opinions, and most of all the way you see.
Looking at the world today, even the United States [in certain states and cities] rejects just about anything that isn't their standard of a proper standing white collared human being. Just look outside and see it.
If only people could just move past this stage, we're all human and honestly so what if there are a load of homo's? They deserve equal rights to love and carry on their life choices it doesn't ruin your life! (=・ω・=) Time to put on another safety pin!
About the homophobia. You guys have to realize that korea (and a lot of other asian countries) isn't like other western countries. They have different views when it comes to homosexuality. It is not as widely accepted as it is in other countries. Some people may like it (hence the yaoi comics) but most people simply don't. I don't like homophobia nor do I condone it but we must realize the context she is in. Its not about double standards or not being supportive enough of her brother, it is simply the culture she was raised in. Now, I'm not saying that makes it all better. Its simply the reason why she acts like that.