In reality, the reason to scold lefty climate activists for overly strident rhetoric is entirely reputational -- it signals your moderation, helps you cozy up to VSPs, distinguishes you from "mere partisans." It's a pure identity play - as pure as they come. HOWEVER ...
...the people most inclined to do the scolding are also the people most inclined to view themselves as above identity, creatures of pure rationality. So they can't admit, to readers or to themselves, the real impetus. Thus, nonsense like, "it gives the other side ammunition."
As though people who watch Fox and elect Donald Trump and bring snowballs to the floor of the Senate to refute climate change are stuck, silent, without arguments, until their opponents make an empirically shaky point. 🙄
As though people who have been accusing their opponents of "socialism" at every single advance in public policy for a century are going to positively reward those same opponents for rhetorical restraint. 🙄
Whatever you think about strident rhetoric from activists, there's just no remotely convincing analysis of current politics that assigns it any particularly significant causal role. If you want to bash it to bolster your identity, go for it, but quit with all the pretense.
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