Just going to summarise the bit I found insightful, because I know some people found the tweet dense:
The basis for this objection [taking platforms, or any kind of financial support, or engaging in joint legal action or publicity, with either Christian or white nationalists] is about the concern that a movement originally grounded in the defence of the interests of women and gay and lesbian people could be co-opted by people who are hostile to the political interests of women and homosexuals.
I agree with this because I've observed MRAs coopting feminist positions and twisting them to be anti women. It is a known tactic and leads to the "but when is International Mens Day" type rubbish.
For many feminist women this is a problem. They fear that the energy of the UK GC movement could be fed into the hands of very powerful, and increasingly dominant, populist forces who will use that against women and gay people and also ethnic minorities.
And I agree with this. In the past we've had the Erin Pizzey/Cassie Jaye type scenario where women who claimed once to be feminist become sympathetic to the MRA agenda and generate headlines/undermine feminist efforts. Personally I can see how populist movements are using the GC concerns to advance agendas that damage women.
As a movement, we have spectacularly failed to discuss either these sets of concerns in anything resembling a calm and sensible manner and have failed to extend good faith to each other over legitimate points of contention. That makes me personally very sad, and politically, I think we are all very much the poorer for it. and yes, bang on. Too much time spent arguing over points of difference in a black and white way, not enough focus on common good actions to support women.