That is to say, I don't really think it's fair to point to those who are going to be murdered by the state and say, "well, if they had just followed my idea"...

It's fair if they are wrong. Allende's death does not absolve him of very clearly and systemically fucking up.

"You will only survive with revolutionary organization and fervor" feels a bit like, "don't siege Leningrad, just take it."

No, it's more like saying "You only have a chance of seizing Washington if you have a revolutionary apparatus with which to seize it, and some socdems in Congress are not such an apparatus, nor a major element of such an apparatus". The Nazi example is ignoring how something is done and suggesting you can just make it so. The criticism here is the opposite, saying that demsoc types have a model of change that is literally nothing more than handwaving because if they wanted to be "socialists" while not handwaving, it would entail some conclusions that they are uncomfortable with supporting, so they don't.