I'm not sure how that happened either. It does seem paradoxical. A lot of the transphobes seem to have mainlined Janice Raymond and her ilk - who is American, after all - and to have stopped there, circa 1980. I often detect a general iffiness about intersectionality, too. But why/how that toxicity flourished in the UK when in other respects - gay rights, for example - the country compares favourably with the US, I don't know.

(My best top-of-head guess about that is that homophobia in the US is often driven by religion, and the UK is not a very religious country; whereas transphobia in the UK is often sustained by cod-scientific arguments with a superficial plausibility to people who don't know much about the subject.)