politics

The other comment is good, but I think there's something larger. Conservative policies are incredibly unpopular, as is the sitting President. However, this doesn't matter if you can mobilize people against a common enemy, and it doesn't matter if that enemy is real or imagined.

Trans people are uncommon enough that most people don't understand that they're perfectly normal people just trying to live their lives, just like they are. It's easy to make up stories about them destroying society, and being the root of all evil, and they don't ever meet a trans person who dispells this idea. This makes them a useful enemy that they can fight against instead of actually doing what benefits the people.

The very short answer? Insecurity.

The slightly longer answer?

Many people get their sense of right and wrong, their morality, their entire identity exclusively from those around them, and never from themselves. They don't even think they are capable of having any of that themselves; mainly because they've been told since they could barely misunderstand language that that's impossible.

If your society disallows personal identity and forces you to pick from a preselected and made set of options then anyone not fitting those options is doing something wrong. Many of them legitimately do not understand why they dislike trans people or gay people or just people that don't fit into the narrow version of society they grew up understanding was the limit of acceptable existence, they just know "it ain't right."

The existence of the Other, especially an Other that is incredibly proud and out about their existence, one who is not ashamed to not fit into any of the available options they've been lead to believe solely exist, physically causes them pain. Because it forces them to question, even subconsciously, if whether or not the entirety of their known existence is actually wrong. Because (statistically) that question was beat out of them at an early age.

Every child, at some point in development, encounters someone outside their "tribe" that they do not understand. They look to those around them for guidance, of course, but if in an independent environment (i.e. a sheltered white child meeting a black child at a playground mostly unsupervised) the child will show curiosity and then acceptance assuming the encounter doesn't end in any perceived danger. That child automatically accepted the Other into their "tribe" without question, because without outside input and without any sense of danger, there's no reason not to; however if that child did have someone in their 'tribe' close by that disapproved, or worse yet explained why they disapproved, that child will associate that interaction as 'outside the tribe' and develop discriminatory beliefs because that new person is not how "they should be." They do not take any of the roles in the tribe that have been explained.

Now modern humans in modern times can break out of "tribal" thought. In fact most will try to at some point, early in their childhood, then again in their teen years, and finally if and when they are placed independently in a new environment in their young adult years (the college effect). But if there's someone there at every turning point stopping them from gaining that independence, they will just withdraw and stay in that simplistic world view.

They are a {straight} {man/woman} who does {tribe-approved work role for gender} and {insert tribe approved weekly cultural activity}. If you differ, you're a danger to yourself and others, and you must be corrected. Because obviously someone taught you to be different. And that someone that taught you was wrong because they themselves were different, and so on, back to {insert cultural reference about warring tribes (i.e. Lilith v Eve)}. You might not even be human.