Funded by the US religious far right...

‘Prove it or shut up.’

But I’m quite rude. Ask him - who benefits from this? Who constantly says ‘no debate’ and tried to shit down all conversations with threats. Who manages to get businesses to change policy and sack staff on their say so - really powerless then? What happens when women’s groups complain or protest (nothing but threats). And why does this happen?

Why would women not want to fight/debate/discuss all this - or should they all just meekly accept and agree? Silly boy - he has no right to a say over women’s issues, he has no idea.

And don’t forget - ‘why would they lie?’ (‘They’ being the people who say this).

Posters have made some good suggestions. Don't browbeat him but say to him that he makes the accusation, he has to supply the proof and it's up to him whether he goes looking or would prefer to take things on faith without checking.

Sow the seeds of doubt and let him mull over why, if he's saying something, he doesn't want to check whether it's true and what this might mean.

Turn off his WiFi - he can't use the internet properly!

Where’s my bloody money then??😆

Seriously though, he makes the accusation, he has to supply the proof! I’d just smile at him and say “I’m sure with all your abilities you’ll find them soon dear”

Painful isn't it. I agree it's up to him to show you, not you 'prove' otherwise.
In the UK this is very much a non party specific issue. Even though it's got more traction in right leaning media, it was a Conservative govt that instigated the review of the GRA.
There are indeed overlaps on this specific issue between the left and right (Communist party are clear on what a woman is).
The UK movement is not the same as the USA.
Maybe point out that most GC organisations are small and there's a lot of successful crowd funding.

One of the things that always puzzles me with this accusation is, if it were true, why are so many women having to use Crowd Justice to raise money for court cases?

Show him the ‘sponsors and supporters’ pages on stonewall, mermaids... websites.

There’s a piece that pops up on twitter on the big pharma companies (doesn’t a trans woman own one?) in the us who spend a lot of money on this arena.

Besides - there seems to be a thing in the US with the religious types preferring a trans child to having a gay one.

If he were my son I would tell him that, as he's the one making the allegation, it's up to him to prove it.

Well can you ask him where my cheque is ?

Can't prove a negative. You can only nudge him to think differently.