Faolyn
(she/her)
Perhaps ironically, the bolded bit is actually the most realistic and plausible way to go. In real life, we can make educated guesses by drawing on our past experiences. But in RPGs, especially D&D, GMs are usually strongly encouraged to shake things up because having similar things happen too often is boring and leads to players getting complacent. In one particularly obvious example, it's why there's so many different varieties of monsters in D&D. Is this slime mold monster the one that dies when its exposed to fire, or the one that aggressively grows and becomes more dangerous? That dragon is green and brown; is it evil, and what does it breathe? Ditto for just about everything else: new interpretations of standard races and adversaries, innovative ways to build your adventure locales, new and different types of traps, and other new twists on old tropes.It seems to me that there's at least 2 lines of argument against a fail forward model, which I'm categorizing as "the argument from naturalism" and "the argument from gameplay."
I'm frankly less attached to the argument from naturalism, at best I think it can serve to make the game state more understandable to the player and avoid negotiation. The idea is that the situation should unfold according to prior inputs and not be causal to a new board state of the result of an action is reasonable just the status quo prevailing. I agree largely with what you're laying out here, that nothing happening is nothing happening as a rebuttal; I don't think naturalism is it's own defense. There should be a gameplay purpose and the only reason I think you'd want a status quo result is to ensure it's understandable to the player. That is, a player can't necessarily map consequences from "I try to pick the lock" to a fail forward result like "the guards hear you and open the door to see what's happening" unless they're explicitly told ahead of time this will happen.
Which brings us to the argument from gameplay, as that immediately creates the grounds for negotiation of either that specific consequence, or for the player to propose a different action to get a different consequence. Negotiation is the death of gameplay, because it subsumes all other mechanics. It always has the potential to be more effective or to overturn any other kind of mechanical interaction, so if it's allowed to creep in, it becomes the gameplay loop immediately.
The negotiation issue aside, fail forward runs the risk of removing tactical agency. If you make players commit to actions without knowable consequences, they lose much ability to discriminate between risks in the first place and it's not necessarily clear that they should prefer picking the lock to having down to the door in the first place.
In other words, unless the GM has a very curated, and above all short list of things the players may encounter, there's not going to be much of a way for a typical party to know the consequences. So "making the players commit to actions without knowable consequences" is, in fact, logical. They've never been in this situation before; how would they know the consequences?
However, in most games, either (a) the players are allowed to make knowledge rolls ahead of time or during the encounter or (b) in games that don't rely on skill checks, the GM is allowed or even encouraged to give the players knowledge based on information written on their sheets or backgrounds. "I have the 'Arcane Botanist' trait. What do I know about that plant-monster?" And that means the players aren't going to go in blind nearly as much as you might think--even if they've never been in this situation before, they probably some knowledge that can help them.