You have to be really attuned to "is this actually rational or sound right, or am I adding in an implicit 'but we're good people, so,'"
It accelerated rapidly with some trends like the Tea Party, Gamergate, Brexit, Andrew Wakefield, covid antivax, and the Ukraine situation, and is in evidence on both sides of the trans rights debate, in doxxing, in almost every single argument on X that goes past ten tweets, etc.
It's something many on the left have generally identified as worse from the right wing or alt.right.
But this is just because it's easier to categorise it when it's pointing at you. It's actually the primary toxicity of all argument in the 21st century.
And the reason is that weaponised bad faith is addictive fun for the operator.
Basically everyone gets to be Lee Atwater or Roger Stone for a bit, and everyone loves it.
It depends a bit by what you mean by left and right, but if you take something like Marxism that was always 100% a propaganda effort created by people who owned newspapers and the pervasiveness of propaganda has been a through line e.g. in the Soviet Union, agitprop etc. A big part of the Marxist theory is that there is no reality, that social experience completely determines everything, and that sort of ideology naturally lends itself to the belief that blankets of bad faith arguments for "good causes" are a positive good.
This sort of thinking was unpopular on the left for many years, but it's become more hip no doubt thanks to countries like Russia and China trying to re-popularize communism in the West.
I think perhaps I didn't really make it totally clear that what I'm mostly talking about is a bit closer to the personal level -- the way people fight their corners, the way twitter level debate works, the way local politicians behave. The individual, ghastly shamelessness of it, more than the organised wall of lies.
Everyone getting to play Roger Stone.
Not so much broadcast bad faith as narrowcast.
I get the impression Stalinism was more like this -- you know, you have your petty level of power and you _lie_ to your superiors to maintain it, but you use weaponised bad faith to those you have power over.
It's a kind of emotional cruelty, to lie to people in ways they know are lies, that make them do things they know are wrong, and to make it obvious you don't care. And we see this everywhere now.