Sissy porn is a type of pornography that involves men dressing up as women and enacting the fantasies they are aroused at seeing done to actual women, or in some cases, children.
I think some tend to dismiss it as the name itself doesn't show the extreme nature of what it entails - which includes bondage and rape fantasies.
The arousal these men experience comes from embodying the various degrees of humiliation and torture that they enjoy seeing done to the subject they pretend to be.
This is what is crucial to understand about the humiliation and castration fetish behind many men who claim to be women: it is not a one-way event.
The fetish is an enactment of how they see women, and the degradation of women that they eroticize. By pretending to be the subject, they are telling us what they like to see done to their erotic target.
On the one hand, they get off on being treated like a woman because they find it to be personally degrading; but on the other hand, they also get off on the dehumanization of women and children.
The mirror has two faces: their personal portrayal of womanhood is the pornified, objectified version of us. At the same time, the fetish exposes what they want to do to us.
I have been mocked for drawing a parallel between porn and men who claim to be women, while the whole phenomenon is widely accepted among such men themselves.
They even write academic papers about this type of content and how it motivated them to take hormones and undergo surgeries as part of a body modification fetish, of becoming the BDSM porn they admire.