Nobody is pretending to speak for workers when they organize themselves in their own workplace. The people who are organizing are speaking for themselves and are reaching out to other workers who might want to join them, as well as reaching out to the general public.

The IWW is a union where even if you don't have a job, you can still be in the union. So, if an unemployed Wobbly gets a job somewhere and then wants to organize at that job, why the hell is that wrong? I guess it's only wrong if the normal thing to do is to be a cynic.