Social Justice is a implementation of Antonio Gramsci's neo-Marxism that shifted focus away from economic towards cultural revolution (because the economic revolution had failed in his time).
Gramsci realized (correctly) that there will be no revolution inside an existing system of what he called 'cultural hegemony' so the culture war has to be won first. That is why SJW attack all established institutions like family, religion (but not Islam), nations, borders, sexuality, historical statues, entertainment, masculinity, femininity, etc.
Breitbart (the man) picked up on that “Politics is downstream from culture” and thus the SJW wars began.