I suppose not too long ago the advancement of gay rights WAS political activism. Before that, civil rights for minorities was activism. Women's rights were activism at one point, too.
But these activists worked hard, fought hard and their particular activism cemented rights and protections for disadvantaged groups into law, so now it can be taught in schools. Because we should be teaching children about the law and to operate within it.
However, this particular shade of activism seems to be intent on raising one group of people above the law. What we are teaching children is not only not lawful, but we are teaching them that it is now perfectly fine to trample over the rights of some disadvantaged groups if it gets in the way.
A lot of teachers have been tricked into thinking it's the same as the gay rights movement of the 80s and 90s - I have heard many people say this, parrot this like a mantra without really examining it. It's a quick and easy soundbite that sounds good but has no basis in reality when examined, like 'rights aren't like pie!' and 'it's the same as when it became acceptable to be left handed!!'