Whenever a religious figure speaks of fire and brimstone, I take it with a grain of salt. Whenever a politician makes the claim that anyone who speaks against them is racist/immoral/greedy/stupid, I tend to think they're frauds. Why would I let the scientists make claims without doubting them? I'm not calling climatologists liars; I'm saying that they're acting like liars.
Can anyone seriously say that evolution is as proven as Newton's Laws of Motion on the scale of billiard table? Or that our understanding of the Big Bang is as complete as our understanding of muscles contracting? So why choose evolution, the Big Bang and the age of the Earth? Don't get me wrong, I think that all three likely happened, but I wouldn't roll them out unless I had a political agenda. I've heard a variety of estimates for the age of the Universe, I haven't heard of anyone contesting the law of conservation of mass. Why not use photosynthesis and covalent bonds as established principles of science?
The central problem with the open letter is that they suggest that all scientists are apolitical and possess peerless moral character. That they can be trusted to police themselves and everyone else should just stay out of their business. Any organization or group that has been given the authority to police itself won't. Just because there's a witch hunt, doesn't mean there aren't witches. Given the trillions of dollars at stake, I'm perfectly happy to have a few annoyed PhDs to ensure public accountability. And government overreach is always a concern, remember that the Australian firewall was sold to the public by saying that it is protecting people from child porn. But somewhere there's a happy medium between anarchy and totalitarianism.