Can someone please tell me what 'SJW' is?
SJW is an acronym for "Social Justice Warrior". It's a branch of left-wing ideology, that revolves around identity politics (gender, ethnicity, race, sexual orientation, disability etc). It's a branch of political philosophy mainly espoused among sociologists and 'gender studies' (read: feminist) branches of academia.
The focus of the SJW movement is to eliminate what they perceive to be relative disparities between groups of people within capitalist democracies, which they feel are the result of systemic bigotry. Also, there is a kind of virtue ethics involved, where the SJW movement feels that certain personality traits result in "unjust" or immoral behavior.
The movement is controversial, because often white, heterosexual men are portrayed as the benefactors of the capitalist system, and are universally criticized as being "privileged". This causes controversy among people on either end of the ideological spectrum. On the right, people feel that the system is meritocratic, rewarding people for risk taking and work ethic. The movement is controversial on the left because (among socialists) working class white men are considered to be as oppressed as working class minorities. Among anarchists, it is also controversial because left-of-center ideologies inadvertently justify obedience to authority, in the name of equality.
And then there's nihilists like myself, who don't believe in Justice. We'd argue that the entire thing is nonsense on its face. But that's a whole other, controversial topic unto itself.