It recycles reactionary narratives around gay people but now about trans people, the most powerful of which is to undermine normalization of gay or trans folks with kids to invent a reality in which it's about talking sex stuff to children. Someone in drag reading books to kids is a way to normalize people that fall outside of cisnormativity. Reactionaries tell each other stories about how it's actually about sex and then with their ignorance happily accept that this also means grooming, it provides a way to avoid dealing directly and solely with the reality that they are opposed to normalizing people who are just wearing different clothes, reading a book, or just existing as an out trans person.

Though reactionaries already have really creepy thinking relating to children and sexuality already and there's a lot to wade through there.

I want to emphasize that this is a universal reactionary behavior - to transfer frustration to made-up bullshit because contending directly with the situation at hand has too much cognitive dissonance with how they view themselves. Self-identified leftists do it all the time, and particularly burgerland leftists, as we fail to actually internalize the idea is criticizing everything that exists, the idea of solidarity, and the relationships we all have to each other, to communities we aren't yet a part of, and our inability to have sufficient impact through deeply ingrained bourgeois mechanisms.