Apparently FPFW cannot be part of this campaign because it might compromise their legal case.
They have, however, been tweeting their support for this campaign.
I have not seen any suggestion that the organisations that have signed up to this campaign are distancing themselves from FPFW.
The fact that they are campaigning in this way does not preclude them supporting FPFW in their legal case.
What is the factual error - and on which website?
"We are each capable of filling in the census as we see fit."
Of course we are.
Some might wish to support the campaign and others might not.
It's a free country - at least as far as this is concerned.