It is not always the case that my enemy's enemy is my friend. These people may agree with us one issue, but they do so for very different reasons, so we really should not be cosying up to them because they do not have the best interests of women (or gay, or BAME people) at heart.
I think this gets to the root of why we are where we are. The division of ideas and policies that align or don't align with other ideas. If you're left wing, it's expected that along with not being homophobic or racist, you will be totally accepting of trans ideology. Conversely, if you are sceptical about trans ideology (because it's anti-woman and regressive), there is an assumption amongst some people that you must also be homophobic and agree with any number of other offensive ideologies.
What needs to be worked on is the idea that a number of ideas 'go together', and that if you agree with one you must agree with some or all of the others.
Of course the other real problem here is that trans ideology seems to have been swallowed whole by both sides as being progressive, instead of being seen for the regressive, homophobic and misogynistic bullshit it really is.