Otherkin
A while ago and sometimes still to this day there are people who make annoying jokes about trans people, comparing them to otherkin as if that invalidates their identities, or treating the concept of assuming one's identity as if it is a reasonable thing to do. Both of these ideas are rude and could hurt plenty of transgender folks, but that is a given. It could also hurt otherkin that genuinely identify with many vast and numerous kinds of identities outside the range of simple binary or dimensional gender. A lot of otherkin identities feel more real to them than gender ever could due to their less psychological nature, such as when one doesn't identify with human bodies. Gender identities that don't match our bodies can lead to a desire for another body entirely but most transgender people seem to still identify as human. There are people who's gender is that of creatures other than humans, sometimes even that of inanimate objects such as robots and even vehicles in one case I heard of. These identities do in fact deserve to be recognized, even if they are only a small part of a whole identity.
Cringe culture has stunted our ability to empathize with others, and our insistence on othering beings that live lives that don't look like ours is holding us back from seeing the real lives we hurt with our negligence, and our insistence to treat all people that don't fall within our worldview as liars. This treatment of people as liars about their own identity is not only harmful, it is indicative of a way of thinking about the minds of people that is toxic and pervasive in most societies since the post-renaissance enlightenment. This way of thinking that psychology like any other science must be understood in its entirety by way of questioning individuals and coming to contrived conclusions about them based on what little information we can glean from the things they say being taken out of context and treated like indicators of their character. It is a dangerous way to think of others and their minds. It hurts all of us, helps none of us, and causes numerous misunderstandings and hateful treatment towards plenty of us. We do not need this way of thinking and we would do well to excise it from our way of thinking.
Secondhand embarrassment doesn't come from a desire to do harm, neither from ill will of any sort. It comes from a desire to not have the one we feel it for end up being bullied or from a fear of ending up bullied ourselves for associating with them. This shows a deeper problem in society than simply whatever might cause one to not want to be human. It shows that we know deeply within ourselves that our society might bully them simply for the way they are. In order to end the phenomenon of secondhand embarrassment, we must end the society that bullies anyone that might be different from what is expected.