Whats with people demanding others to describe as anti-zionist atm?

Online it seems like a lot of commenters are demanding figures in the Corbyn party, such as Corbyn, Sultana, and Hussain, and to a lesser extent figures in the Greens too with Polanski and Ali. With these people getting nasty if people refuse?

Absolutely makes sense to be very critical of Israel’s genocide and apartheid, and to be supportive of Palestinian self-determination they’ve been denied, but surely it doesn’t matter how they self-describe as long as they’re showing that crucial solidarity with Palestinians?

Is it just purity testing, or is there something I’m missing?