I am going to do my best to address each of your questions, Lucca:
"How do you determine whether someone has DID or whether they are transgender, then? Based on what I've read, DID has very different symptoms than being transgender does, to the extent that I'm not sure how they're being confused."
The short answer is whether transition helps a person's condition rather than hurts it. The difficulty in determining whether someone has DID or whether they are transgender, is that DID is a "disorder of secrecy." Victims had to hide what they were doing from their perpetrator. As such DID masks itself as a variety of physical/physiological disorders or a persons feelings and memory of their abuse may be contained in one of their alters. Sometimes an opposite gender alters need to express themself can be so strong they will insist they are transgender.
Transsexuality shares many symptoms with DID and other trauma related disorders resulting from sexual abuse. Transsexuals also experience gender dypshoria, sexual confusion and the feeling of having been born in the wrong body for as long as they can remember. They were bullied and did not fit in with other children who were the same assigned at birth gender. Transsexuals often struggle with the idea they are transsexual, are survivors of childhood sexual and psychological abuse, and suffer from the very same psychological conditions DID uses to mask itself (depression, PTSD, bipolar disorder and schizophrenia). Transsexual people can even have Dissociative Identity Disorder. My female alter, Flytrap, started a thread for people who are DID with opposite gender alters (both transgender and cisgender) at:
https://www.susans.org/forums/index.php/topic,218553.0.htmlIt can take years of therapy for a person to "slip" or feel "safe" enough to let down the wall enough that it becomes apparent they have DID (average time a person is in the medical system before receiving a diagnosis of DID is 10 years). In my case I was in therapy 2 1/2 years before the time/memory loss, night terrors and flashbacks associated with DID began. That was the missing link that made it clear to my Psychologist my female alter's need to express herself had been misdiagnosed as transgender Gender Dysphoria.
"The way you phrase it, saying DID is more common than transgenderism...The statistics don't bear that out."
Actually, they do. 1% to 3% of the population have Dissociative Identity Disorder according to The International Society for the Study of Trauma and Dissociation. About the same as the number of people who are gay/bisexual.
http://www.isst-d.org/downloads/guidelines_revised2011.pdfOnly 0.6% were estimated to be transgender in the Williams Institute's landmark 2016 study.
http://williamsinstitute.law.ucla.edu/wp-content/uploads/How-Many-Adults-Identify-as-Transgender-in-the-United-States.pdf"you make it sound like %50-%60 of people with dysphoria aren't actually transgender, and shouldn't transition, and if they do it will result in a bad outcome."
Sadly people jump to this conclusion but they are not my words. The purpose of this and all my posts is to make people aware there are other reason besides being transgender they may need to express themself as another gender. NOT to invalidate anyone's transgender identity.
"If there were a lot of people whose gender dysphoric symptoms could be treated without transitioning, I'd think we'd either see a much larger range of accepted, working non-transitional treatments for dysphoric people, or we'd see a much higher regret/failure rate for transition."
The stigmas associated with having a mental illness are strong. The transgender community fought hard to make it clear that GD, not transsexual, is a disorder. Unfortunately this is not the case with DID. The only effective option at this time is therapy combined with psychotic medications. I suspect the rates of failed transition/transition regret are low not because of transition, but because the required screening therapy prior to transition prevents many people for whom transition is not right from transitioning in the first place.
Our couple's psychologist explained to my wife and me her biggest red flag I had experienced childhood abuse was my insistence on how perfect my childhood was. When the time/memory loss, night terror and flashbacks began, it became clear I had developed DID because of this abuse. My greatest concern through it all has been my Gender Therapist's insistence I was a transsexual in denial and her relentless encouragement that I transition, when I was CLEAR, from day one, that as right as it felt to express myself as a woman, it felt equally WRONG. I am 100% unmistakable cisgender male, would NEVER want it to be any other way. How could it not have seemed odd that there was no learning curve for me to be woman? That I had absolutely NO problems fitting into society as a woman and people saw me as a woman the first time my female alter walked out the door... a year before I even started hormones?