SAN FRANCISCO — Cynthia Nixon learned the hard way this week that when it comes to gay civil rights, the personal is always political. Very political.

The actress best known for portraying fiery lawyer Miranda Hobbes on "Sex and the City" is up to her perfectly arched eyebrows in controversy since The New York Times Magazine published a profile in which she was quoted as saying that for her, being gay was a conscious choice. Nixon is engaged to a woman with whom she has been in a relationship for eight years. Before that, she spent 15 years and had two children with a man.

"I understand that for many people it's not, but for me it's a choice, and you don't get to define my gayness for me," Nixon said while recounting some of the flak gay rights activists previously had given her for treading in similar territory. "A certain section of our community is very concerned that it not be seen as a choice, because if it's a choice, then we could opt out. I say it doesn't matter if we flew here or we swam here, it matters that we are here and we are one group and let us stop trying to make a litmus test for who is considered gay and who is not."

To say that a certain segment of the gay community "is very concerned that it not be seen as a choice" is an understatement. Gay rights activists have worked hard to combat the idea that people decide to be physically attracted to same-sex partners any more than they choose to be attracted to opposite-sex ones because the question, so far unanswered by science, is often used by religious conservatives to argue that homosexuality is immoral behaviour, not an inherent trait.

Among the activists most horrified by Nixon's comments was Truth Wins Out founder Wayne Besen, whose organization monitors and tries to debunk programs that claim to cure people of same-sex attractions with therapy. Besen said he found the actress' analysis irresponsible and flippant, despite her ample caveats.

"Cynthia did not put adequate thought into the ramifications of her words, and it is going to be used when some kid comes out and their parents force them into some ex-gay camp while she's off drinking cocktails at fancy parties," Besen said. "When people say it's a choice, they are green-lighting an enormous amount of abuse because if it's a choice, people will try to influence and guide young people to what they perceive as the right choice."

Nixon's publicist did not respond to an email asking if the actress wished to comment on the criticism.

While the broader gay rights movement recognizes that human sexuality exists on a spectrum, and has found common cause with transgender and bisexual people, Nixon may have unwittingly given aid and comfort to those who want to deny same-sex couples the right to marry, adopt children and secure equal spousal benefits, said Jennifer Pizer, legal director of the Williams Institute on Sexual Orientation and the Law, a pro-gay think-tank based at the University of California, Los Angeles.

One of the factors courts consider in determining if a law is unconstitutional is whether members of the minority group it targets share an unchangeable or "immutable" trait, Pizer noted. Although the definition of how fixed a characteristic has to be to qualify as immutable still is evolving -- religious affiliation, for example, is recognized as grounds for equal protection -- the U.S. Supreme Court still has not included sexual orientation among the traits "so integral to personhood it's not something the government should require people to change," she said.

"If gay people in this country had more confidence that their individual freedom was going to be respected, then the temperature would lower a bit on the immutability question because the idea of it being a choice wouldn't seem to stack the deck against their rights," Pizer said.

Nixon stirred the identity politics pot further when she explained in a follow-up interview with The Daily Beast this week that she purposefully rejected identifying herself as bisexual even though her history suggested it was an accurate term.

"I don't pull out the "bisexual" word because nobody likes the bisexuals. Everybody likes to dump on the bisexuals," she said. "But I do completely feel that when I was in relationships with men, I was in love and in lust with those men. And then I met (her fiance) Christine and I fell in love and lust with her. I am completely the same person and I was not walking around in some kind of fog. I just responded to the people in front of me the way I truly felt."

Although science has not identified either a purely biological or sociological basis for sexual orientation, University of California, Davis psychologist Gregory Herek, an expert on anti-gay prejudice, said Nixon's experience is consistent with research showing that women have an easier time moving between opposite and same-sex partners.

A survey Herek conducted of gay men, lesbians and bisexuals of both genders bore this out. Sixteen per cent of the lesbians surveyed reported they felt they had had a fair amount of choice in their sexual orientations, while only five per cent of the gay men did. Among bisexuals, the figures were 40 per cent for men and 45 per cent for women.

What remains to be teased out, Herek said, is how a representative national sample of heterosexuals would answer the same question, and what people mean when their sexual orientation was a choice or not. Are they talking about their sexual desires? Acting on those desires? Or simply the identity they choose to show to the world?

"The nature vs. nurture debate really is passe," he said. "The debate is not really an either/or debate in the vast majority of cases, but how much of each. We don't know how big a role biology plays and how big a role culture plays. A possibility not often discussed is it's not the same for everybody."