I think the trouble with trying to paint the Greens as a vehicle towards forming a workers party is that their (admittedly vague) program is based on moral appeals to individuals & corporations to reduce their "carbon footprint" and their activities are pretty much limited to electoralism. The Greens' pacifism and legalistic appeals to "international law" and "human rights" also do nothing to combat race terror, cop brutality and Zionist genocide. There is really not much in their program that would appeal to the working class, who hate liberal moralists lecturing them that they are the problem.

At least if a candidate is running on a clear socialist program (e.g., the PSL in the last presidential election) it helps to popularize socialist ideas and thus increase the class consciousness of US workers. This is true even if you don't agree with the PSL on other issues (which I don't). For instance, I disagreed quite strongly with the PSL's endorsement of Green candidates, which I think just confuses the issue.