They can't imagine that gay people understand it better than they do. They dig in their heels and build their little fortress and it's the Band of Straight Brothers, shoulder to shoulder against those "homosexuals." How could a "homosexual" possibly know more than they do? Whatever knowlege those homosexuals claim to have is just, by definition, homosexual knowledge, tainted by their sickness and therefor highly suspect, probably subversive and easy -- perhaps mandatory -- to reject.
This is something else that also parallels well with autistic people - It's amazing how often someone who is very ignorant of autism, even when their only reference is Rain Man, to say things about autistics with this tremendous air of authority, and get angry at the suggestion that reality may in any way deviate from that.
(digression: One crucial similarity of gay kids and AS kids -- which makes our minorities very different from racial or religious minorities -- is that we are almost always born into families that do NOT want us to be what we are. Black kids are not born into families that desperately do NOT want black kids. Jewish babies are not born into Baptist families. So black klids grow up with black parents who teach them to love and respect themselves for being black. Jewish kids are taught to revere their identities and traditions. Like gay kids, most AS kids are born into hostile territory.)
Yes, this is one area (amongst many) that I am very fortunate, as my dad is autistic and both parents are accepting of autism and gayness.
It is a little exceptional that a straight person honestly wants to learn much truth about "homosexuals" -- not even to learn that we don't like being called "homosexuals" -- and exceedingly rare that they have any authentic understanding of how homophobia or heterosexism works.
Interestingly, as I am pretty young and didn't grow up in a time when it was medically acceptable to medicalize homosexuality, but I did grow up hearing kids use the word "gay" with derision at me, other kids, and things, I remember being quite surprised to learn that homosexual is not the preferred term. Then I started reading up on a lot of things, and it started making more sense.
Certainly not if it means they have to question their own unimpeachable attitudes for any trace of prejudice or that they might have to admit vast ignorance and have to be schooled by people they consider their inferiors.
As a white person, I was trained to have that same attitude toward black people. As a male, I was raised and socialized to view women the same way. As an NT, I was acculturated to believe myself intrinsically superior to the neoro-divergent. I was certainly raised to be a homophobe, and I was pretty damn good at it.
At various points in my life, I came to realize I had to seriously and diligently un-learn this crap that was pounded into my head all my life. In order to do so, i had to cop to the truth that I was racist, homophobic and neuro-supremacist.
My question used to be "Why doesn't everybody get honest about their prejudices and ignorances, and seek out people who can teach them otherwise?"
But the more I see, the question has become "Why do some people get honest, face their prejudices, and do thge work to un-learn them?"
I think it's largely due to people always wanting to be right. Some people grow up beyond that, though aspects of this desire exist in less severe forms even in very mature people. Some people though, they grow up believing the world is a certain way, this initial impression of a worldview usually being very much shaped by societal and family prejudices, and so they are more likely to look at this as the foundation of what they know about reality is.
I think that's one reason why there's so much resistance to accepting autism, because even though there are autistics who aren't disabled in their current situation, people need to confront their ignorance and stereotypes of disability - it's these false assumptions about disability that cause people who are skeptical of the idea to change it into false dichotomies (such as thinking that we are against education/treatment/services, or that there's no downsides, or that you need to be highly intelligent/functional/whatever in order to not want to get rid of autism).
Likewise, a person grows up, exposed to certain views of sexuality, and they get an idea of homosexuality as an embarrassing deviance, and if this gets challenged, it can't be because their original conception was wrong, but it must be because the other person is being "too sensitive" or "paranoid", seeing insults where the first person just sees their worldview, which CAN'T be flawed or mean - no, because everyone knows that they're just so nice and wonderful and born perfect in every way. Even some people who will say, "oh, I know I'm far from perfect" act like they're perfect anyway; I know because I've been that way.