Going to respond to this slightly out-of-order because it will flow better that way.
You're objectively correct with this statement....and I never said anything contradictory to it. Far from it. I pretty much explicitly said otherwise. However, I find that the costs of saying "no" too often are much, much, much worse than the costs of saying "yes" too often; I find that DMs are much, much, much more prone to saying a flat unequivocal "no" when they should have said some variation of "yes" (or at least "no, but...") than they are to saying some variation of "yes" when they should have said a flat unequivocal "no"; and that players in general respond very negatively to even a very slight excess of flat unequivocal "no" answers, while even an egregious excess of some variation of "yes" is far from guaranteed to cause a problem.
Point being: "Yes" is something DMs need to learn to use, whereas "no" seems to be the default for situations the DM wasn't already well-prepped to respond to, and that both the benefits of saying "yes" in the cases where you definitely shouldn't say "no" far outweigh the costs of saying "yes" when you shouldn't, and the costs of saying "yes" when you definitely should have said "no" far outweigh the costs of saying "no" when you shouldn't.
In general, some variation of "yes"--usually "yes, and" or "yes, but", or occasionally "no, but", which is functionally a "yes" answer along a new/different/alternate path--is simply better. There absolutely will be times when you should just say a flat "no." But those times should be exceedingly rare. Like "a couple times in a year of weekly games" rare. If you're needing to say a flat "no" more often than that, something is seriously wrong and you need to have a heart-to-heart with your players to figure out where and what the disconnect is.
Well then, Ms. Silverman's mother was a good person. Honesty isn't just the best policy, it's the only policy. But it's also only the first step on that policy. As the Good Book says, we must speak truth in love. That is, lying never serves love--but as an old friend of mine once said, "The truth is not an excuse."
That's the critical bit missing here with the analogy from "always be honest" to "always make sure the players earn their fun". It has to be reasonable, achievable, actually "fair" in the way people usually want "fair" to mean, that is, giving folks plenty of chances even if they've foolishly ignored/overlooked/simply missed previous ones, adjudicating based (at least in part) on what was intended and not (exclusively) on what was actually done, giving folks ample time and space to explain themselves, and meeting them at least halfway if not much much more than halfway, etc., etc.
In other words, something that doesn't really look "impartial" at all, except for from the perspective of the participants themselves. Because what feels impartial, and what is actually impartial, are often two very different things. As is the case with so much of the stuff in this conversation, what often (not always, but often) matters is not the absolute truth of the situation, but the feeling of having a thing. The only place where both the feeling and the fact matter equally is agency itself, hence why I've spoken at length about the problem of invisible railroads and illusionism in this context.
I've had a similar situation to your previous example. I had prepared this (I presume!) awesome encounter where several blood-obsidian spirits (long story--TL;DR: they're not-technically-undead wraiths made by evil druids binding the still-technically-living spirits of sapient beings to a sufficient quantity of ground-up blood obsidian) had been accidentally melted by soul-animated mechanical spiders (whose bodies were designed to be destroyed by their own flames); in the conflagration, because of the similar magics involved, the two opposing forces had fused into a towering molten-obsidian golem with mythril mechano-spider-leg claws coming out of its "hands".
And then they just...retreated and taunted it into walking into a pit trap full of water, which solidified it and they shattered it with a single weapon strike. I simply hadn't considered that possibility, they had, and although I felt a bit embarassed at having failed to foresee such a thing, my players loved that they'd figured out something clever. Talked about it for months after (not in a "haha see how we pulled one over on you" way, but rather a "that was AWESOME" kind of way).
So I very much understand where you're coming from on this. My problem mostly arises with...well. Taking the thing too far; shutting down too many plans because of an excessive commitment to realism over fun, treating the rule of cool as something absolutely verboten rather than a useful tool to be applied when appropriate and to be left aside when inappropriate. I've had both bad DMs I've personally dealt with and DMs I've heard horror stories about from my personal friends (not just randos online, who can say whatever they like even if it's pure fiction) who have taken "realism before fun" WAY too far. From that, it is my considered belief that taking this too far is both extremely easy to do--as in, it's one of the hardest-to-resist DM temptations out there, second only to the temptation to force outcomes to go the way you designed them to--and extremely easy to ad hoc justify when one should not have done so.
I can only speak to what I do and what I've enjoyed. If someone attempts something that I think clearly isn't in the spirit of the rules I will ask them what they're trying to accomplish. Then we'll see if we can work out something. Frequently it will be something they can attempt to get some advantage but there will be a penalty if they fail. So they may be able to jump down from the tree they're hiding in to attack an enemy, but to do so they have to go to the very edge of the branches and if they fail and acrobatics check they'll fall and land prone. If it does work I'll give them advantage on the attack. In the case of the players discussing options like sneaking past the guard I give them all the details I think the characters would know. If I think there's something the players might notice I'll be generous with whatever check makes sense.
So yes, I'll give players information because it makes sense for what their discussing or give them chance to notice something they aren't thinking about. I want the players to succeed and have victories. I just want them to earn it, even if I give them a hints here and there, other times I'll go back and clarify something just in case I didn't make something clear.