This is part of my "Fantastic Primer" series, which incorporates a few fictional elements. In particular, if I were to write a real 101, it would be much shorter and to the point. Please read the introductory post, which explains the premise.
Asexuality and Alien Abduction
If you hold skepticism as a virtue, then one of your first reactions to a new concept may be, "But is this actually true?" After all, the profoundest truth is laid low by being false. About asexuality, you may ask, "But does the asexual orientation exist?" The very question may seem rude to asexuals, but I know you're not trying to be rude. You're not trying to be in-your-face about it. It's just the question that comes to mind.
I put forth that the answer should be a swift "Yes." Asexuality is manifestly real. Lots of people experience it. For those who don't experience it, asking asexuals about their experience is a legitimate way to study the subject. No, seriously, if you look at the small body of research on asexuality, the researchers basically consider it obvious that asexuality exists, and they study the subject by asking asexuals and non-asexuals about their experiences.
If you're unsatisfied with self-reported evidence, consider a comparison with alien abduction experiences. We know today that most alien abduction experiences are caused by sleep paralysis hallucinations. I once had such a hallucination, although I didn't think it was aliens, I believed a burglar was pinning me down. The point is that these experiences are real. Alien abductees are not liars. They just misinterpreted their experiences.
Asexuals are not misinterpreting their experiences, because they are not interpreting them at all. Asexuality is defined as the experience of not having sexual attraction. It doesn't matter what the underlying cause of the experience is, we're still experiencing it. I really don't know what the underlying cause is, but it's probably different for different people.
Often people propose that asexuals are really just sexually repressed. Besides being a meaningless and unfalsifiable explanation, it doesn't even invalidate asexuality if it's true. If it turns out people are asexual because some chemical interaction is blocking their sexual attraction, that still means they are not experiencing sexual attraction. The main difference between calling it asexuality and calling it repression seems to be that if you call it repression, you're assuming something about the cause, and making a negative moral judgment about it.
People also propose many other causes for asexuality, like hormone problems, abuse, anxiety, autism, and schizoid personality disorder. I'm afraid none of these really stand up, in that none of these characteristics are particularly dominant in the asexual community. I would be open to good studies showing a connection, but my money's on a more complicated set of causes. In any case, people are still asexual regardless of cause.
Stability, and Identity as a Tool
There's a difference between repression and asexuality that I overlooked. If it's a matter of repression, you might predict that it's something you can get over. Can asexuals "get over" asexuality? That's not really something I can answer without some serious research. But you could draw parallels to conversion therapy, intended to convert gay and bisexual people to straight. Not only is it pseudoscientific and harmful, the problem it tries to solve is not really a problem. Likewise, asexuality does not really seem like a problem to be solved. Even if it were, conversion therapy sounds like a very bad idea unless there's very strong evidence for it.
More generally, we could ask how stable the asexual orientation is. Do most people who identify as asexual continue to identify as asexual years later? I haven't seen any research on this question, so I don't know about the statistics. I know lots of people who have identified as asexual for many years. I know people who looked back on decades of their life, and realized they were asexual even if they didn't identify as such at the time. I also know people who stopped identifying as asexual, either because they never were, or because something shifted in their life. I know people (including myself) who changed to gray-A or demisexual identities, both of these being between asexual and non-asexual. I know people who considered that they might be gray-A, and then decided they were just asexual.
And all of these identity trajectories sound fine and good to me! Even though asexuality is attacked all the time for being an illegitimate orientation that will evaporate away upon the first sign of a hot stud, I'm still fine with people shifting their identities when necessary. An asexual identity isn't a commitment. It's a tool to understand who you are. Sometimes people may get it wrong, but it's not some unmitigated disaster because people generally figure it out for themselves.
The asexual community generally tries to facilitate people figuring themselves out. Introspection, and detailed analysis is fashionable. There's active discussion about what it means to be between asexual and non-asexual. People feel free to express their doubts. There's a lot of uncertainty involved in asexuality, but asexuals deal with it in healthy ways.
What's unhealthy is the way that everyone else constantly questions the validity of asexuality upon first encountering it. Somehow it fails to fit in their worldview, and people just deny deny deny.
What asexuality teaches us about reality
Once you get past the questions of existence and validity, the next question is what we can empirically observe about asexuality. This is my favorite part! The fact of the matter is that some things about asexuality are rather counterintuitive and surprising. There are things that you simply could not know without asking asexuals.
For example, is sexual attraction a required component of romantic relationships? The answer is no, because some asexuals want romantic relationships. In fact, asexuals frequently speak of a "romantic orientation" such as heteroromantic, homoromantic, biromantic, panromantic, and aromantic. Romantic orientation specifies which genders you're interested in romantically, or if you're not interested at all.
Is there a difference between a strong friendship and a romantic relationship, besides the sex that is usually involved? Yes there is, and it's quite clear to some people. But there are also asexuals who have trouble distinguishing the two, and who don't identify by a romantic orientation for that reason.
Does a lack of romantic feelings impact other emotions as well? No, clearly not. Aromantic people can certainly feel connected to people, and don't lack emotion.
Is masturbation necessarily attached to sexual attraction? No, it's not. Some asexuals masturbate, and some don't. This is one of those rare questions where I don't just have anecdotes, I have studies. That means that instead of just talking about what experiences are out there, I can talk about the relative prevalence of the different experiences. Studies show that asexuals masturbate at rates that are only slightly lower than non-asexuals. (Yes, some non-asexuals also don't masturbate, and I don't like to joke about it.)
Does not having sexual attraction lead to repulsion to
sex, or indifference? Some asexuals feel repulsed, and some feel
indifferent. Some would be willing to have sex in a relationship, some
would consider it a deal-breaker. And a small number of asexuals enjoy sex
(which is consistent with research showing that people have sex for lots of reasons besides sexual attraction).
How does asexuality interact with gender? No one knows, but the information we have so far is intriguing! Asexual women outnumber men in the community surveys and in the national probability-sample surveys. In-community surveys also show relatively large numbers of people with non-binary genders (~25%). It's unclear at this point whether this reflects any underlying reality or if it reflects the numerous sampling biases.
Are people really bothered by lack of sexual attraction? Yes. Most asexuals I have spoken to have experienced various levels of denial and prejudice. It's hard to tell how much, since existing research is limited.
Asexuality teaches us many facts about reality, and also offers some intriguing clues to human sexuality. Next time, we'll learn a bit about the structure and history of the asexual community.
A paper discussing what it means to call homosexuality a disorder, the thrust being that there's a subjective element.
My thoughts on asexual doubting
My bayesian analysis of asexuality, an example of the kind of detailed analysis I said was fashionable in the asexual community
The Fantastic Primer series:
2. Why I don't trust you
3. Yes, I'm one of those atheists
4. A skeptically-oriented Asexuality 101
5. Atheism as minority, atheism as political cause
6. Atheism and asexuality: a historical comparison
7. Why atheism and asexuality taste great together