It certainly can be used as you described, but it doesn't have to be. I sort of loosely define an SJW as someone who 1) believes that the law should be wielded

It certainly can be used as you described, but it doesn't have to be. I sort of loosely define an SJW as someone who 1) believes that the law should be wielded to enforce their version of morality, 2) that the correctness of their morality justifies pretty much any means of attaining it, and 3) that doing anything to further their goal is always preferable to doing nothing to further their goal, even if a specific thing is likely to have adverse consequences. That's a pretty broad definition that almost includes religious people on the right wing of the spectrum, and that's pretty much what I would say is the only difference between a Social Justice Warrior and a Religious Justice Warrior--the source of where they validate their brand of morality. Other than that, they are approximately identical in both their methods and the extent to which they are damaging to liberal democracy. I recognize that this is probably not a very common definition, and your point about SJW being a meaningless insult is likely the correct one.