>Those on the left also quite often suffer from letting perfect be the enemy of good.

Exactly, its because they are idealist. Its also not hard to follow this observation over to Europe, pretty much the epicenter of idealism on earth, and then look around. Oh yeah, much more liberal than the US, with countless examples of idealism throughout. One of the current such examples is how Europe sees Putin, and how the East sees him.

The antidote to the idealism are individuals with confidence, and of course testosterone. Elements which when put in a pot with the aforementioned mix violently. You need people saying, well, this is good enough, and if its not I'll come up with something that'll fix it, when that happens.

As usual, a mix of both is needed.