Urriak Uruk
Gaming is fun, and fun is for everyone
If the expectation is that you're in a game where your choices matter, then it's dysfunctional. If that's not your expectation, if you expect to be moved along the plot in a timely and entertaining manner and just visit the shops along the way, then, yeah, cool. But it's kinda like promising Risk and then playing Candyland.
If we can stick to "railroad" as a verb, it's inherently dysfunctional. The DM has a script for what the PCs do, the players try to do something else and the DM railroads them, forcing them back onto the script. There can be some built-in remediation through Session 0s, social contracts and whatnot, but I don't think that makes it any less dysfunctional.
The thing is, despite the length of this thread, I've been playing for 40 years with all kinds of players and I've yet to encounter one at the table who likes being railroaded. I've met plenty who are resigned to it when it happens or just don't care because they have other priorities (e.g. getting to the next combat), but I've never met anyone in an actual game who enjoys being railroaded.
Ah, so you're saying railroading is dysfunctional when players try to "leave the tracks." Well, yeah. I agree with that. It does add more meaning to the word railroad than it actually has, but I guess in a gaming context people assume that this will always exist.