Like most problems in the world, the SJW movement has been perpetuated by American culture and ignorance. I believe the whole Gamer Gate, started by Anita Sarcosy is what really brought the SJW shitheads out of the woodwork.
I'd also argue that the lack of debating ettiquate so visably present in American media is the reason why these people cannot be talked to. Watch CNN or Fox compared to the BBC and you will see what I mean. American's don't debate, just shout over one another.
I appreciate my views are likely influenced by my own strong anti American biase, but I firmly believe that the route cause of the SJW movement does come mainly from all the negative aspects of American culture, and has spread because of Americanisation in our own cultures through the acceptance of American media, American influence in our news and the internet.