Holding gender critical beliefs isn't at all similar to racism.

With racism, the racists are denying other people's humanity, based on race. That ideology centres around the notion of a group of humans being somehow subhuman.

This isn't the case with 'terfs' - they're not denying or diminishing anyone's humanity, they're simply saying that whether you're a woman or a man is determined by your biological sex, rather than a proclaimed gender identity.