How did this terminology occur, what is the connection with actual postmodernism, why should we avoid to connect this world with legit online activism and what does Jordan Peterson have to do with it?

The Word postmodern and it’s abbreviation PoMo is used as a downgrading label for every kind of social activism, so called “social justice warriors”, members of the LGBTQ-Community and identity politics. How did this terminology occur, what is the connection with actual postmodernism, why should we avoid to connect this world with legit online activism and what does Jordan Peterson have to do with it?