Let's say that scientists determined with certainty that pistachio is the best flavor for ice cream. Pistachio ice cream lovers everywhere would no doubt scream, "I told you so!" and many people might switch to eating only pistachio ice cream. Those of us who dislike pistachio ice might be a little skeptical of the settled science, but we probably wouldn't much care and would continue to enjoy other flavors. The pistachio ice cream lovers might then call us skeptics or deniers and look down on us from their moral high ground.
None of this would much matter, unless pistachio ice cream lovers and scientists latched onto politicians (or vice-versa) to have the government ban (or at least tax and regulate) all flavors of ice cream other than pistachio. This clearly crosses an important line since one group is now limiting the subjective choices and opportunities of the second group. Yet nobody was ever stopping anyone from eating pistachio ice cream.
Now substitute "something should be done about global warming" for "pistachio is the best flavor for ice cream". The substitution, while having elements of absurdity, works surprisingly well.
Even if one accepts that global warming is happening with certainty, and even if one accepts that the scientific consensus is that something should be done about it, once that group forces its subjective preference for doing something on the rest of us, a very serious line is crossed.
It's the line of oppression and totalitarianism.