For a start, you have misunderstood this:
"Everybody on this forum is certain. Dead certain. Xx Is female and Xy Is male. There is only this."
If you actually asked instead of thinking you are posting great and intelligent 'gotchas', you would actually get some answers that would show this is actually not the full story that you are trying to make it. Chromosomes are just one aspect of who is and is not female. The expert biologists tell us that usually this chromosome categorisation is reliable. However, what is the appropriate statement is that a female person is someone who is born with a body formed around the production of large gametes, meaning having ovaries or that the body intended to have ovaries where there are not gonads present, regardless of whether those large gametes were ever produced, are being produced or will be produced in the future.
"There is no gender."
When considering single sex provisions, gender is irrelevant except for if an additional gender neutral provision is needed. In which case, that is for those needing that provision and the groups that support them to campaign for.
"Usage of a sexed space must rest entirely on the makeup of your blood: your chromosomes."
The usage of a sexed space must rest entirely on a person's sex. As per the body formation categorisation mentioned.
"I find this reductive, naive and discriminatory. It forces people to use spaces designed for their sex at birth when they might have been identifying otherwise for decades. It might terribly humiliating not to mention risky, to walk into that space and be a target for bigots or macho drunk guys. But this, you say, is the price of your kind of absolutism. (The fact that it is someone else's price to pay, and not yours, is just by the by)."
So, a group of people have been using spaces that they should have respected were for the opposite sex to them for decades. And you don't see a glimmer of colonisation in your statement.
Why should a group who should have remained out of the other sex's single provisions be allowed to continue to enter after it has been shown that not only do female people feel distressed by male people being in those provisions they need to be female only, but also that this is all driven by a person's philosophical belief.
Just to be clear again, there is no biological or neurological markers that can be used to categorise someone who has a transgender identity.
'It might terribly humiliating not to mention risky, to walk into that space and be a target for bigots or macho drunk guys."
Firstly, please show the statistics in the UK where male people with transgender identities are at risk of being attacked more than any other group of male people in the UK population.
And if you cannot, why does this group of male people get special treatment over the other groups of vulnerable male people. That is actually direct discrimination.
Secondly, 'It might terribly humiliating not to mention risky, to walk into that space and be a target for bigots or macho drunk guys." This is not for female people to solve by allowing any male person to access single sex provisions.
Thirdly, if a male person is going to targeted specifically because he is trans, what is to stop those attacking male people coming into the female single sex space to attack that male person? Your logic simply does not hold.
"But this, you say, is the price of your kind of absolutism. (The fact that it is someone else's price to pay, and not yours, is just by the by)."
Safeguarding protocols could be said to be 'this kind of absolutism'. No male people above 8 years old to be using the female single sex provisions.
"The fact that it is someone else's price to pay, and not yours, is just by the by"
This is just pure emotional manipulation and it is actually not even true.
A group of male people with transgender identities don't have to use female single sex provisions. There are plenty of gender neutral options available to them. If they choose to reject the single sex provision provided for them though, that is something they must address themselves - without disrespecting the needs of female people in the process. Which is what you seem to be pushing for on this board -that female people have to accept male people into our female single sex provisions and that this is the only acceptable solution.
That 'absolutism' about who must use provisions, seems to be all yours.
This is the type of inconsistency that we have been trying to point out to you.
I will come back to the other paragraphs.