Oh my, what a topic! Allow me to shed some light on this. To be able to answer this question properly, research must be done. History must be read, religion must be discussed, etc.
One of the reasons homosexuality is hated is because people fear it. Ever heard the saying "What we do not understand, we destroy"? It is all so very true! People, typically Americans and Mexico, are fairly adamant about hating gay people because they may look strictly to the bible for answers and completely ignore understanding.
(For the record, religion enables us to enjoy the lack of understanding)
For individuals, secondly, it may be for personal reasons. Maybe someone felt insecure and vulnerable around a homosexual. In other words, some people are afraid they may LIKE being gay. And well, lets face it... being gay in religious areas has its consequences. This fear may be reinforced by siblings, parents, friends, elders, government and/or religion. To counter ANY chances they may be gay, certain individuals will be very aggressive towards gay people, thus justifying themselves and their homo-free life.
Well, I can go on. Anyone want to add something else before I do?