The word "homosexual" has become a pejorative term for gays and lesbians. Those who are anti-gay always use the term "homosexual" and never "gay" because they say there is "nothing gay about being a homosexual," and that homosexuality is a choice, which we now know is not true. In fact, those who are anti-gay believe that homosexuality is always a sign of pathology. The New York Times recently ran a great article on this issue, "The Decline and Fall of the 'H' Word."
Given this truth, why do the media give a platform to those with anti-gay opinions whenever gay issues make the news? When someone makes a statement that is racist or anti-Semitic, the media don't contact individuals from the Ku Klux Klan and say, "We will hear next from a doctor in the KKK to hear his opinions." So why are those who clearly believe that homosexuality is wrong allowed to wield the "H" word against us in the mainstream media?
Although the term "homosexuality" is still used, using the word "homosexuals" for gays and lesbians is now as offensive as using the words "Negroes" or "Coloreds" for African Americans, or "cripples" for people with disabilities.
Similarly, terms like "sexual preference" and "alternative lifestyle" are no longer considered appropriate, because "preference" and "lifestyle" imply that one's sexual/romantic orientation is a choice, which it's not. For gays and lesbians, heterosexuality is the "alternative lifestyle."
The negative connotation of the word "homosexual" initially came from its prominent use by anti-gay religious denominations, and from its use in early psychoanalysis. (Before the 1970s it was widely believed that one could change from gay to straight. While there are still individuals who believe this today, they are a dwindling minority.)
Referring to someone as having a homosexual orientation is OK, but saying "homosexuals" or "he is a homosexual" is offensive. If you come across something in the media where the word "homosexual" is used, especially as a noun, you are most likely reading something anti-gay; in the best-case scenario, the author, journalist, speaker or reporter is simply ignorant of the negative connotations of the word.
The gay and lesbian communities each use different terminology and jargon. Of course, some overlap exists between gays and lesbians, but each group has its own unique slang, "code" words, and euphemisms, and in cases of overlap, the terms may have different connotations for each community.
Over the years, other minority groups have changed how they want to be referred to in an attempt to change how they're treated. For example, African Americans went from being called "Negroes" and "Coloreds" to today's more politically correct "people of color."
Today the word "queer," historically a pejorative term, is often used by lesbian, gay, bisexual, and transgender (LGBT) people in a positive way, just as the pejorative "N" word may be used by African Americans. Dozens of books and articles are published with "queer" in the title.
It is always best to ask a person how they self-identify and use the same terms that they use, even if you feel uncomfortable with those terms on a personal level.
For example, I personally don't like to use the term "homosexual," but when clients of mine identify themselves as "homosexual" and state that they dislike the terms "gay" or "lesbian," then that's the word I use when I sit with them. To me, the word "gay" is affirmative and describes a life of being out and open about one's sexual/romantic orientation. However, many people in the beginning stages of coming out feel uncomfortable with the term. Similarly, some lesbians prefer to be called "gay" rather than "lesbian," whereas others find the term "gay" offensive when used to describe women.
It is also important to understand that some "reclaimed" terms used by gays and lesbians to refer to themselves are considered offensive when used by straight people.
For example, some lesbians call themselves "dykes," and some gay men call themselves "fags," but these same lesbians and gay men would take offense if a straight person called them that. (In fact, there is some disagreement in the gay and lesbian community itself about these terms, with some gays and lesbians finding them offensive regardless of whether it's another gay person using them.) In these cases, straight individuals should not use that terminology, just as a white person should never use the "N" word, even if some African Americans use the word themselves.
If you are unsure about whether you're using a term that might be considered offensive, it is best to not use it until you have established a rapport and can ask the lesbian or gay person how he or she feels about your using it.