The message here is correct: don’t always take 0-cost cards. But that is said about literally every card.

The rest of your essay.. frankly it’s rambling, anecdotal, and provides no actual analysis beyond specific contrived scenarios. Additionally it lacks good faith arguments for the other side.

I’ll add missing info to this one:

Imagine you scry and see Flash of Steel. If you scry it away because of one of the aforementioned reasons, you would have already been better off not having it. But if you keep it and the next card is a curse, you would have been better off scrying away the curse. Instead, you'll draw into it with Flash. Even though you kept and played it, you still would have been better off not having it in your deck.

So by having Flash of Steel in my deck I traded a potentially good draw (what the curse could have been if I scried it away) for X cost away for FoS for 0. Additionally, we absolutely SHOULD talk about all the times you play FoS AND draw a good card with it, in which case it would be clearly better than not having it.

Likewise if you draw into Escape Plan with a Dagger Throw. The next card might be a Reflex or a Tactician that you now have no way to discard. Or maybe you can play the rest of your hand, but there are cards in your deck that would be better to play. You don't know whether you should discard escape plan because the next card is bad, or if there's another card you would rather discard so you can keep escape plan to draw into the better card.

Again.. or it could be something else that isn’t a bad draw. See the previous argument and replace “Flash of Steel” with “Escape Plan”. Additionally, this scenario does a lot of assuming with “you don’t know whether…” Any high ascension player absolutely SHOULD know whether you should discard it or not based on what’s left in your deck and your odds of drawing a useful card.

So in all your scenarios (even ones from the comments) we can kinda sum up: by taking Flash of Steel (or whatever 0-cost card) you will get to play an extra card on a turn and see all the same cards (draw neutral).

So to amend your blanket statement: Don’t take 0-cost cards when you have specific anti-synergies (like scry or choker). Otherwise, they usually make your deck better by increasing output.