Just because we cannot guarantee certainty or outcomes doesn't absolve us from the moral responsibility to try.
When PG says that the left and right are equally "wrong", he's suggesting that they are both trying to arrive at THE solution, but just taking different paths. I don't think this is fundamentally true and if you view political struggle from this perspective you're going to miss the full picture.
So yes, both the extreme left and the extreme right are not only wrong, but morally repugnant.
The whole point of classical political liberalism is of how to get multiple incompatible ideas of what is the good life (broadly understood) to coexist peacefully. Without it there is only tyranny or chaos.
I think the point is that different people will try different things, often opposing each other.
For example, let me grant you that Nazi Germany and the Soviets were equally bad for the sake of this question, would that mean that we and our allies were moderate? Do the proxy wars that we fought/are fighting all over the world factor into an ideological spectrum?
The reason that I'm asking a question instead of just going all "what about-ism" is I really would like top understand why people think the way they do. Not trying to start an argument.