How come it's so hard?

Why is it so hard for people to accept other people for who they are? Or parents to accept their children for that matter? Why should I have to fear my parents judgement?

I realize that many people might have written on this subject already but maybe someone can help me out. I'm bisexual and all my friends accept me for this, but I know my family will never be able to. That's sad that they can accept other people but not their own daughter. The only person in my family that I've told is my older sister and she and I are basically twins. If anyone would understand I knew that she would, so tell me what went wrong. After I came out to her she acted as if the world were going to end. She started crying and yelling at me like it was my fault, as if I could help it. As of now she's gone into a state of denial and won't ever bring it up again. Her forced ignorance is the thing that bothers me the most about this. She has plenty of gay friends, does she think that just because she's related to me that she'll be bi too? I don't know what's going on with. If I can't even tell her how am I going to be able to tell my parents? I don't want to have to call them up 10 years from now when I'm possibly thousands of miles away to hear them whine and bitch at me.

If anybody has any sort of advice please enlighten me because I don't want to have to go on lying to my family for the rest of my life or theirs.