I say you're projecting an identity on a group of people you label as SJWs because I don't know if the group you think exists actually exists in any cohesive manner. Also, it's a bit like "racists" or "misogynists", most of the people you would put in the group probably wouldn't think they belong there. Often, I suspect the term is used to identify "people who have called me racist or sexist".
You don't know if the people exist. I do know they exist - I've observed them and identified them by their actions.
You can dismiss the label all you want - people use words to describe the world as they see it. Your inability to adopt a different perspective does not make that perspective wrong or nonexistent.
As far as I know there is not. There are people who use the terms too freely, but as far as I know, they are not part of any organised effort to police public behaviour.
Organized effort is not part of the definition. Irrelevant objection. Is there a concept of "Social Justice"? Yes/No. Are there people who fight for that concept of Social Justice? Yes/No. An individual fighting for Social Justice is a Social Justice Warrior. He doesn't have to be part of a group to be an SJW. Whether all SJWs are perfectly agreed on every ideological point is also irrelevant. There's a general trend that can be described.
Recently, a scientist was called out for being sexist because he wore a shirt covered with sexually dressed women. Regardless of whether you think that is a good/bad thing - there was action by a group of people to police his behavior, and an effect where he publicly apologized for wearing the shirt.
The people who think that calling for an apology on sexism is more important than landing a spaceship on a comet are most definitely SJWs by action and belief - they value Social Justice over scientific achievement, and they act accordingly.
I'm not arguing that the term needs to be changed. After all, what would be the point? I'm saying it is already effectively meaningless, much the way conservative talking heads have made liberal and progressive meaningless by ascribing it to virtually everything they don't like.
Liberal and progressive are not meaningless labels - do you think "conservative talking head" is a meaningless label? Why would you use that term at all if you think liberal/progressive have become meaningless labels? Only conservative talking heads have preserved meaning?
You yourself criticize groups for being "called on attitude" and "believing ... conspiracy". You certainly believe that groups worth criticizing exist - just not the ones you don't criticize. Why the bias?