Or in 2020, when Bernie won a whopping 26% of the vote?

Setting aside establishment collusion because I'm sure you've read that Jacobin article already, 26% percent of the vote is enough to "capture a small enough portion of your voting base that covers the margin of victory (aka: the short hairs) and demand the party do your bidding". If you disagree with that strategy your argument is with the parent comment, but the condition was fulfilled in 2020.

Alright, but considering that many groups involved with the Uncommitted movement ended up, afterwards, explicitly saying "Don't vote for Harris"...?

What, exactly? You're not making any point.

It's complacency - a complacency that is enabled by progressive detachment from Dem politics.

How in the actual fuck is 26% of the vote (after ridiculous amounts of sabotage, mind you) detachment? That's more than twice the proportion of progressives in the Democratic Party (p.96).

Considering that many of them were and remain useful idiots peddling the exact same talking points now as they were then about how voting is implicitly (or sometimes explicitly) worthless?

Why do you feel the need to respond to statements of fact with moral condemnation? That could be true and it would have no bearing on my argument.

rarely did it drop under 50-50, and the asspat brigade was always there to fluff them.

It depended on the community, but on mainstream communities it was a lot more than "rarely". Source: I was one of the ones getting downvoted and flooded with a hundred versions of the same three arguments. That was about the time I lost faith in American democracy, and certainly not because I was getting upvoted when saying progressives needed to pick more fights with the DNC.

they were overwhelmingly lost from young, progressive voters who cited progressive issues as their reason for not voting for Harris.

Where did you get "young, progressive"? In battleground states the economy was the top issue according to your own link, and as I said before there's no guarantee that all or even most Gaza non-voters are progressives. Yes, opposing genocide isn't a moderate position, but it's not like progressive politics come as one prepackaged set. It's not like Midwest Arabs suddenly became progressive overnight.

Leftists who claim to believe otherwise and then act in direct contradiction to those stated values are a bit more jarring.

That's not the point. Since it's mostly moderates who dropped the ball, the anti-leftist crusades are beating a dead horse, alienating potential allies for no real purpose and a fundamental misunderstanding of what makes leftists an (occasionally) effective political force. Hint: It's not sheer numbers or pandering to the establishment.

There's a loud and influential anti-Democrat minority whose effect is multiplicative on the already small turnouts of Dem primaries.

This argument would hold water if the "mainstream" progressive narrative was anti-Democrat, but with that decidedly not the case non-voters were people already predisposed to coming to that conclusion for one reason or another. You'd need to completely eliminate anti-Democrat rhetoric to have a shot at keeping those people, which would entail creating a pro-Harris walled garden that realistically cannot exist. Leftwing dissent isn't even your biggest problem here; Republicans are always out there happy to exploit the Dems' political weaknesses, and good luck getting those Arab-Americans to shut up about all those funerals they keep attending and the disdain they keep receiving from the Democrats for it. Remember who organized and formed the core of Uncommitted? The "ideal" (I personally consider it dystopian) environment you're gunning for is a fool's errand because unfortunately America happens to be a society.