I am a leftist, and agree that many of them don't act in a good faith, for exactly that reason. However, I recently watched (for a reason I won't go into here)

I am a leftist, and agree that many of them don't act in a good faith, for exactly that reason. However, I recently watched (for a reason I won't go into here) Nelson Mandela talking about apartheid, and why he accepted support from communist dictators such as Castro or Khaddafi, when it was clearly in bad faith. And he explained that he is looking at it solely from the perspective of ANC goals, and the dictator's (material) support for their cause. So this got me thinking, I as a leftist do not define my identity around a cultural or ethnic group, and I instead ground my identity around moral universalism of human rights. Which means, I have to reject guilt by association, because in some sense, I am not loyal to any group. Even if you only support free speech, you should reject guilt by association, because it makes engagement with the opposing side impossible. So I don't really see how supporting a declaration I pretty much agree with can hurt the cause, despite the fact I think some of the signatories are acting in a bad faith.