Why do some people care if people are gay, lesbian, or transsexual?

Many people were raised with a religion that states homosexuality is abnormal and a sin

I don't care. The only time I care is if a girl is flirting with me or asking me to be with her and her boyfriend. Yes that actually happened lol

i believe 'live and let live.'
however, i don't think it is good or wise to instill the idea in young people, or anyone else, that sexual inclination/orientation is from Nature, and that this is an "Identity" that defines one as a human being.
sexual orientation is both genetic and social- no one can untangle it, at least for now, maybe they shouldn't.
the ancient Greeks had same-sex relationships, then later got married to women. "Gay" is from the 20th century. I think classical Greece and Rome, as well as other European and Middle Eastern cultures, proves that homosexuality/bisexuality is not solely a product of the genes and/or hormones.

Im not a saint and I dont throw judgmental stones