They're sometimes the same people who may move from Miami to Seattle, and suddenly find themselves having to be more aware of their language. The term 'SJW' has a particular dynamic that makes it somewhat unique, but usage is not entirely dissimilar from the pejorative use of words like gay, retarded, and others along those lines. Widely stigmatized, especially in more liberal areas (rightly so), but still has a lot of cultural currency.
SJW is just widespread enough that it can exist in a space outside both liberal and alt-right bubbles. There are plenty of people who use it casually, without the level of meaning those groups tend to infuse into it. So when I see someone use SJW, assuming a relatively innocent context, my most comfortable assumption is that they're uneducated on the full dynamics surrounding the term.
And I'm coming from a place where I can relate to that. I started browsing Tumblr because I was interested in their social justice communities, and bounced after I got tired of all the vitriol. I did a Google search on the phenomenon of childish Tumblr leftists, and soon after was introduced to the term SJW. At the time, it seemed quite fitting. Eventually, I saw that some of the people using it were garbage human beings, and I dropped it from my vocabulary.
