I strongly dislike and disapprove of the usage of terms such as "SJW" by people who are attempting to make a serious point on a particular issue (as opposed to a tongue-in-cheek one).
I do not believe that labels are always a bad thing. They are often necessary for the purposes of self-identification, for instance; it is a better idea to state "I am an X" on your "About" page than to bombard visitors with an essay about your beliefs. However, when you are debating or voicing your grievances on one particular issue, pinning the other side down to a very broad label is intellectually lazy and dishonest. Take, for instance, this top comment regarding the #Shirtstorm controversy:
It implies two things:
1) all feminists agree that the shirt was wrong.
2) all of the feminists who agree that the shirt was wrong are in perfect harmony in regards to their motives, level of agreement, and desired outcome.
Neither of the above assumptions are true. The comment is a wholly unjustified attack upon all of feminism based on nothing more than a few articles and tweets. It is, to put it quite bluntly, a circlejerk post, designed to appeal to a person's biases rather than their sense of reason.
"SJW" has it even worse than "feminist", partially owing to the fact that "feminist" has, at the very least, a somewhat concrete definition. "SJW", on the other hand, is a very nebulous term, and can be easily manipulated without the potential threat of someone correcting your definition. Liberals use the label as a pejorative against extremists. Fascists on Stormfront use it as a pejorative against anyone to the left of Goebbels.
Human beings are complex; each of us are unique in our thought processes, beliefs, and attitudes. Even a movement that seems as simple and straightforward as social justice activism ("equality for the disadvantaged") harbors a constellation of factions and competing ideologies, many of which can be understood only by those willing to dig beneath the surface.
Applying terms such as "SJW" to someone despite knowing close to nothing about them outside of a single opinion; treating all of the people with whom you disagree as some swarming "other" lacking in individuality; drawing conclusions about a vast, complex, and multi-layered ideological movement based on a handful of partisans in an ultimately minor conflict… these are all signs that a person has not dug beneath the surface, has no respect for their opposition, and is ultimately more interested in partisanship than the truth.
The solution is to identify sides on an issue-to-issue basis. For instance, a sizable chunk of self-identified conservatives support (or are neutral on) gay marriage, while a small portion of liberals oppose it. Something along the lines of "same-sex marriage opponents" ("SSM opponents" for convenience) would thus be a more accurate label for people who disagree with the legalization of gay marriage than simply "conservatives".