I used to think this. I don't know anyone who would think twice about someone being gay. It's a privileged situation to be in to be honest.
Homophobia is still around. In all of our living memories, gay people have fought and won rights that they should have had all along.
It's lucky for you that you are in a situation where you see homosexuality as mainstream, but that's certainly not the case everywhere.
Finding opportunities to show children from the start that being gay or having two mums or whatever is normal is really important.
Not long ago, when I was teaching, a little boy asked his Dad at the Christmas fair if he could have his nails painted at the Y6 stall. His Dad replied, "No you can't you little f*ggot."
I'll never forget it. Blistering homophobic cruelty.
So back to the rainbow face paint. I'll say it again. Take it at face value. The staff aren't teaching the children about scissoring. It'll be that face paint a nursery-accessible way of starting to introduce children to that people can love who they want.
You're the ones conflating being gay with the trans agenda.
The staff aren't making it political. You are.