Note to the Reader: I'm using a fairly broad brush in my analysis. If something doesn't apply to your individual experience, please do not feel offended - this is a very high level view of things, and is not intended to cover every possible situation.
As the title suggests, this is a foray into an area of discourse that is potentially quite volatile.
Over at Véronique's place, the subject of whether it makes sense for Transgendered and Intersex to be 'tacked onto' the GLB movement came up in the comments. What follows are my own thoughts on the matter of whether "T and I" belong with "GLB".
I think this discussion exists on biological, social and political levels, and there are no absolute answers where these axis of information intersect.
The science today is inconclusive about the causal factors involved in transsexualism. However, there is a growing body of evidence that hints at biological factors that affect transsexuals (over at Zoe's place, she has more of the evidence summarized. This lends some weight to those who argue that Transsexualism is closer to the Intersex than it is to the GLB side of the equation.
There is a dark irony in this logic though, for the GLB communities have long argued that they were "born this way", an argument that similarly asserts a biological essentialism that I think is hard to ignore.
I do not want to lean too heavily upon a purely biological explanation at this time either. There are too many psychological factors at play that influence the development of personality and identity. Our understanding of those processes is far too limited to rule them out entirely in favour of the appealing essentialism that biology provides for. As I have argued before, biology is not destiny, and we should not by any means assume that a biological explanation is the only valid, conclusive underpinning for the condition.
Unlike many Intersex conditions, which have fairly clear physiological markers, transsexualism may only ever be described as a coincident grouping of loosely related markers; and the broader range of transgender expression probably never will be adequately explained in any cohesive sense. (Note: This does not imply that I think that transsexuals are "more valid" than other parts of the transgender spectrum, rather that I suspect that the biological understanding of transsexualism has a greater chance of being described by science.)
Socially is where the T and Intersex have more in common with each other than with the GLB population. Common social interests bring the GLB communities together socially. The very natural drive to find a partner in life gives a great deal of fuel to the social engine of the GLB communities. A relatively small minority in the general population, there is compelling reason to associate with each other, producing a fairly coherent sense of community.
Where the GLB community has a very natural reason to associate with each other socially, the T "community" is actually so broadly defined that it is in fact a mosaic of multiple distinct populations. While transgender support groups do exist, and they are in some dimensions social in nature, they are far from representative of the overall transgender population. The transsexual population is conspicuously absent from the membership of most of these groups. For a variety of perfectly valid reasons, a lot of transsexuals all but disappear off the community radar after they have transitioned - blending into the fabric of society. The transgender umbrella does not cover a coherent social community at all.
My experience with Intersexed individuals is admittedly limited - I've known one or two people who have told me that they were, but as far as I know they live pretty conventional lives as part of the broader society, and beyond political/medical advocacy do not seem to form social organizations per se that are focused on their status as Intersex. (a pattern which I find intriguingly similar to the general patterns describing transsexuals post-transition)
From a social perspective, although I accept that the GLB and T/I communities intersect, I do not think that they represent a logically coherent social community collectively. (even though the Gay Male subculture has a long history of Drag) Where the social fabric of the GLB communities has evolved on shared goals of socialization, the Transgender community intersects with the GLB for far different reasons. Certainly, the GLB community is more accepting of transgender people socially than much of the straight world is perceived to be, and that is particularly valuable for those who desire a social environment to express their identity, one should never lose sight of the fact that the underlying objective of (for example) a crossdresser is simply to socialize in their adopted gender, and they are not necessarily interested in a partner relationship. Complicating things further is that a Crossdresser who is "out" at social functions may still fear discovery by peers from other parts of their life such as work. These factors all contribute to a relatively superficial degree of integration between GLB communities and the Transgender community.
I have to imagine that unless someone who is IS happens to self-identify as GLB, that the interface between GLB and IS populations is even smaller than it is with the transgender population, and that those few IS people who fall into that category would integrate reasonably well since their social objectives would be fairly consistent with the GLB community as a whole.
Politically, there is an entirely different dynamic at play. For a variety of reasons, the public perception is that transgender behaviour is a form of sexual behaviour. Part of this is due to the long standing association between gay male culture and Drag. Additionally, it has taken the high side of thirty plus years to get most people to disassociate sexual identity from physical characteristics (and even at that, there are many who deny that distinction's validity), in many respects this is only just beginning with gender identity. In this respect, there is a cold, hard political reality that transgender issues are firmly embedded with GLB issues in the public arena. I do not believe that it is feasible to change this in the foreseeable future.
The second point is that the kinds of systemic discrimination that GLB and T/I folk experience are fairly consistent, and in general I doubt that there is any significant disagreement with respect to objectives. Nobody should be fired from their job, or denied access to medical care because of their gender or sexual identity.
Yes, the political goals do diverge in some respects, but the underlying goal is to erase the systemic discrimination that allows the obstacles to exist in the first place - at least forming a reasonably coherent political lobby based on common interest. While GLB people are currently heavily invested in the struggle to gain legal marriage rights, T people are struggling for other rights - such as the right to change the gender marker on official documents like passports and birth certificates. These are somewhat divergent objectives, but it is hard for me to imagine any reason why there would not be shared support, as both ultimately achieve the objective of making it easier for members of the respective communities to live their lives in peace.
The Intersex raise some interesting arguments with respect to individual autonomy and access to medical treatment. One of the most interesting bits of advocacy that I have seen from the IS community is the demand that IS children not be surgically altered until they are old enough to make the choice for themselves. I find this argument to be quite interesting, as it asserts that the individual should have the choice as to their physical status based on how their identity evolves - it is a line of argument that in many respects is parallel to the demands of transsexuals vis a vis medical treatment.
Yet, I can also appreciate that many IS folk would be uncomfortable with being associated with GLBT advocacy though. Even more so than for transsexuals, the experience is distinctly not related to sexual identity, and to tie their political objectives to the GLBT lobby creates a secondary perception in the public mind that many could perceive as deeply troubling. (In many respects, the perception that transsexualism is somehow related to the broader picture of GLB sexual identity is quite troublesome for many transsexuals)
Many IS folk no doubt experience much of the same systemic discrimination that GLBT folk experience - difficulties accessing appropriate medical care; hostility or friction if their gender status becomes known and so on. (What goes on an IS person's driver's license?, and how readily can they change that to reflect their reality?)
The mistake many make is in assuming that GLBT (and I) are in any respect a cohesive community on any level. At best, it is a social mosaic brought together by common cause and large scale misconceptions in the public understanding. Where there is strong common cause - for example legislation against discrimination - there is good reason for all of these communities to come together and insist upon inclusiveness. A piece of legislation like ENDA which does not include transgender and intersex folk is a deeply flawed piece of legislation, and one that perpetuates the very mythology that has been used against GLB people for centuries. (I was not impressed when I saw HRC agree to a transgender exclusive ENDA - that was not a constructive act
I can see T and Intersex issues (mostly access to appropriate care, and personal autonomy) as intersecting quite appropriately, and it is quite rational to argue that there are strong parallels in the obstacles that people face, whether they are trans or IS when interacting with the medical professions.
Shared political causes does not, however, mean that each of the populations has to feel a sense of social connection to the others. This is perhaps one of the most vexing aspects of the entire discussion. We have several disparate populations that should share a great deal of common ground politically, but share only limited social commonality.
These groups need to learn to work together on the political matters, and shed the implicit expectation that there is any need for shared social experiences. Further, the public needs to be educated actively about all three groups in a constructive manner, as it is in many respects public perceptions that have thrust the groups together in the first place.