[user104658]

Honestly I think Corbyn just thinks that this idea is populist and fits with the image he's trying to project. He thinks it's a left-vote-winner and recently my opinion is that there's actually not much more to Corbyn than that... He would stand up for the rights of mosquitos to bite malnourished children if he thought the mosquitos would vote.

However I think he has drastically misjudged the situation... It's a very, very small niche that actually thinks this is a good idea. Most I would say are supportive of fully transitioned transgender people using the bathroom they want to use... But the idea that this should be extended to people who are not physically trans is not a popular one at all and is going to alienate a lot of his core voters. The idea has placed feminist and trans rights activists - who would normally stand on the same side of the equality / rights fence on the vast majority of issues - at each other's throats in such a way that I'd say it's almost as if it's by design... "make them fight each other and they won't have time to campaign for anything else".