>>1 because you said to base our ideas, here are mines:
Before I start I wanted to say that I didn't want hurt anyone or to tell which is wrong and right =)
Some people thought being gay or lesbians are wrong because:
a. It is not normal for them. Everyday people saw couples as a pair of a boy and a girl. When we were still kids, we watched tv, read books, listened to musics, etc. about a love that can be only shared by boys to girls and girls to boys. It became implanted in their heads that this is right, others was wrong. It became their ideals. When they knew a person didn't think the same as they did, they thought it is wrong. It is weird. It is disgusting. They wanted to fix it no matter what to fit their ideals.
b. Religion values. Christians (I'm one too) believed that God had made Adam and Eve, man and woman, to complete each other. Not man and man or woman and woman.
Genesis 1:28
God blessed them and said to them, “Be fruitful and increase in number; fill the earth and subdue it....
This bible verse told that God want us to increase in number and to do that it requires a man and a woman.
c. other reasons I don't know about (personal issues, troubles, etc. involving gays and lesbians)
Some people thought are fine with because:
a. they knew that the person had awful experiences that lead them to liking their own gender (I read it in a newspaper once about a girl who's traumatized by boys and liked girls now instead)
b. the person can't help it, they cared too much about that person (best friends or something alike) and thought that feeling was love
c. (again) other reasons I don't know about
Personally, I don't think homophobic or being gay or lesbian is wrong. If they can't and or won't change themselves, it is fine.
Everyone wanted to feel love and to be loved back, and everyone had their own ways to achieve one.
(Wow, I am rambling :D, please pardon me if my beliefs are wrong, I am just sharing thoughts)