Hmmmm...well one reason certain people don't like LGBT people is the fact that it's against their religious beliefs. I don't know other religions as well as I know Christianity so I can't really say what those religious texts state about homosexuality, but according to the bible liking the same sex, or even thinking about the same sex in a perverse way (perverse meaning anything other than friendly) is a sin and might result in going to hell if the person doesn't change their ways. One thing religious people fail to realize is that GOD DOESN'T HATE HOMOSEXUALS!! It's true he DISLIKES their ways (choosing to continue to sin instead of asking for forgiveness and such) and wishes they'd "see the light and repent" but as long as those who choose to stay homosexual don't relinquish the hold the devil has on them then God can't do anything/ AND I know I used the word choose because people aren't born homosexual, bisexual, lesbian, or wanting to be transgendered, you have a moment where you can decide to seek out the word of God and ask him if you should be doing this or that (like we're suppose to do with everything) but you don't and continue to live in sin. The devil doesn't mess with people he already has meaning if you are feeling confused or accepting being LGB then God probably has a big plan for your life that you won't get to know cause the Devil has lead your astray.
So other than LGBT being against God and of the devil, another reason people are homophobic is because it's taught to them. Generation after generation will pass on good and bad knowledge to the new ones. Racism will be passed along with pride, as will acceptance be pass along with homophobia. I have a lot of homophobic family members and gay family members. People might have a best friend, cousin, etc who gay but the world goes by "the exception to the rules" meaning you'll accept your friends or family if they're gay, but other gay people you'll harass or shy away from. You know your friends and family, but the other gays are strangers and don't deserve your respect is basically how it tends to work.
People fear the unknown. And what is "known" (mostly lies and the like) are that LGBT are molesters, rapists, etc. They'll do the freaky things "normal" heterosexuals wouldn't do. I have plenty of gay friends and don't believe in judging people since it's only God's job to judge anyone. The bible teaches us to be tolerant but many interpret the good book to mean whatever they want it to mean.
I used to be bisexual, and I still sometimes am tempted to sin, but nobody said salvation was simple and easy. I made a personal choice to reacquaint myself with God and to stop disrespecting him by blatantly living in sin.