People can lie. People can likewise lie about being gay. They can lie about their religion, and even in some cases, can even lie about their ethnicity. Sometimes it's easy to tell it's BS, sometimes not. This doesn't strike me as a particularly convincing reason to curtail the ability of sincere trans people to be recognized as their self-identified gender.
You keep trying to hide the issue. It's not about "recognizing" their "self-identified gender". It's about whether or not to allow them to access sex-segregated spaces. Don't obfuscate that.
And let's take a moment to consider why someone might lie. A cismale predator might lie about being trans in order to access female-only spaces and commit mischief. This is undesirable, is it not? You said you don't care about consequences, but other people, including me, do, and it's never going to work to demand that we don't.
Is there an equivalent problem with lying about sexuality? Not really. Certain spaces cater to homosexuals, but admitting straight people doesn't cause problems (aside from possible discomfort for the straight people). And other than dating sites, I can't really think of spaces which cater specifically to straight people, and if you're gay, why would you even want to access those spaces?
Race, though, is an interesting example. And you will notice, people get very upset about it when people lie about being a minority. I think it's a little off-topic here so I don't really want to go into it, but I don't see how that example indicates we shouldn't care about the veracity of claims regarding trans status.
Evidence is lacking that gender-fraudsters is a significant problem in places with self-ID. Time will tell, but I think the danger of this is mostly imagined.
Possibly. And if that turns out to be true, it's perhaps your best argument. But the data isn't in yet to really support that claim. And absent that data, I don't think caution is unwarranted.
Consequences have practical impacts that may have to be mitigated, but adverse consequences don't impact whether or not an underlying assertion is true. The adverse (to some eyes) consequences of "trans women are women" is irrelevant to the question of whether or not that statement is true.
At the end of the day, the truth of falsity of "trans women are women" is always going to be a semantic debate, and those are always the least interesting debates to have. It is true for some definitions, and false for other definitions.
But the choice of definitions is not actually the important issue. The actual important issue is what we should
do, and that isn't uniquely determined by which definition we choose. The fight over definitions is useful to each side to the extent that it can influence people's choices, but that's not a logical connection, it's an emotional one. So we are still left with the question of how transwomen should be granted or denied access to certain female-specific spaces. And possible adverse consequences are VERY relevant to that question.
There's a huge difference between reasonable accommodation for disabilities required by law and the language of anti-discrimination law. The language of anti-discrimination law is much stronger and affords much more. Trans people stand to get much more should gender identity be afforded protection under antidiscrimination law.
I don't think anyone here has opposed antidiscrimination protection for things like employment and housing. But granting those doesn't require that you grant them similar legal protections in terms of accessing bathrooms, sports, prisons, etc. Extending sex discrimination to gender identity is very easy to justify. But by the same token, allowing gender identity discrimination where sex discrimination is allowed (or just not allowing gender identity to override legal sex discrimination) doesn't present a slippery slope.