Torah: I was kidding… (If you’re kidding just say so and ignore everything below.)
What on EARTH does a peace sign have to do with a rainbow?
A peace sign is a representative of a fifty-year-old peace movement that is pretty much irrelevant right now to the extent that nobody even remembers what a peace sign stands for anymore.
A rainbow is representative of a movement that the principal would definitely see as against TORAH. Not against conservatism.
There is nothing in the Torah forbidding liberalism (sorry, Yated). There is a lo sa’asay in the Torah against the basics of what a rainbow stands for.
Setting aside the fact, of course, that nobody would say boo if a bais Yaakov girl wore a rainbow because around here, LGBTQ is not the first thing you think of when you see a rainbow.
I think people are more disturbed by the pop culture aspects of peace signs. By the same token, they may have issues with mustaches now (which is a rant for another time).