Do you forget that there are those crediting the New Deal with deepening the Great Depression? Perhaps we'd more easily learn from history if there were not two versions of it.
Does all those who want things bad for the country and good for a few have to do is put up contrary claims to muddy the waters?
I'd say that arming for WWII made us more vulnerable, fighting Vietnam saved Vietnamese lives, creating the FDIC created risk for small savers, allowing unlimited money in politics reduced corruption, ending slavery reduced freedom for blacks, giving women the right to vote took away their political power, making gay marriage legal discriminates against gays.
There, how's that. I guess there's no lesson from those issues, since there are two sides being claimed to them.
The point is that a side is right and a side is wrong, much of the time - the fact that there are perverse, wrong, contrary people who claim the 'other side' doesn't make you have to say 'there are two sides so no lesson there'. It's usually a bit more subtle - a nugget of truth exaggerated into a lie.
Take Bill Clinton's budget - rarely have we had a clearer test of economic policies than his first budget, when every Republican on record predicted doom for the economy if it passed.
It did and the opposite of what they said would happen happened. So where's the accountability? Where are the people who got it wrong learning a lesson?
They didn't say what they say to get it right - they say it to get your money. And so they just kept making the same false claims to get your money ignoring the facts.
And it worked. Much of the country went right on listening to them because that's how propaganda works.
They'd come up with new names for it from time to time, but it was the same wrong policy sold for decades and decades and still is. That's a point of this thread.
What policies took us to the great depression? What policies took us out?
Sadly, the voice of the propagandists whose policies are set by what benefits the rich and powerful is much louder for many Americans than the voice of who's right on the policies.
Paul Krugman has been called 'the guy who is always right', and he does have many years of getting his economic predictions correct against wrong right-wing ideologies.
But the advertisements for the hucksters are well-funded and continue to dominate our policies.
So the fact there are some propagandists and wrongheaded people who say wrong things - climate change deniers is just one example, with your Great Depression example - doesn't mean they are correct. You are raising a question whether democracy can triumph over the special insterests' lies, and the answer seems to be, rarely.