It can't be. Many, MANY of your examples of railroading, aren't railroading and don't meet my definition.
They in fact do. If they don't then your definition actually has some extra personal caveats that you are hiding, which is probable, which means you are the one with a private and personal definition. But feel free to explain why my examples don't meet the stated definition.
Hell, you've stated that the DM asking, "Are you sure you want to do that?" is railroading, despite the players being able to say yes they do OR no they don't. The DM is failing there to force the players down path of his choosing.
LOL. Seriously, metagame direction like that were you influence the players choice is a really powerful railroading technique. You are manipulating the player's decision making process. I can't understand why you don't see asking that question is anything but a GM attempt to control the player's action because he doesn't want the player to do that. And sure, the player can say "Yes, I do.", but like the second or third time a player says, "Yes, I do." and terrible horrible things happen to the player character, they are going to take the hint.
For it to be railroading, the DM needs to refuse what they players have chosen to do, and force them down a different path of his choosing to get them to where he wants them to be.
The thing is your definition of railroading is just confined to DMs doing it crudely and ineffectively. You only understand it as railroading if it's just some crude "No, you don't; you do this instead." contest of wills or something. But the crudeness and bluntness of the application of force isn't part of your definition. The difference between what I'm seeing and saying and what you are seeing and saying is I recognize that artful, clever, subtle and economical applications of force to make the players go where he wants them to be, and invalidating their choices on where they decided to go, are just as much agency removing as direct confrontations and in fact are much more likely to be successful in manipulating the game and the players in the long run.
UPDATE: And additionally, to just show how ridiculous the definition offered by
@EzekielRaiden is in this example, by his definition when I train my players to say "No" by asking them "Are you sure you want to do that?" and do something else I prefer, by his definition they aren't being railroaded because they have fully informed consent. "Thank you for taking my agency away, Mr. GM."