Morkus from Orkus
This is the one area I've seen where you and I disagree. So long as the players have a choice, an encouraged hook isn't a railroad. There has to be no choice or invalidated choice(like the quantum ogre) for there to be a railroad. I've seen players turn down a tempting hook a number of times. That's not a railroad.Sure, most is probably an overstatement. Though even a non-railroad can be a railroad in the hook. For example you can have a dungeon adventure that is pure exploration but the hook is presented in a way where it pushes the players to get in the adventure itself (I don't think railroad is just about structure, it is also about the GM insisting the adventure he or she has in mind will occur, and pushing the players back 'on track'). But like I said it also boils down to execution. Though I was thinking more about modules that have paths or events. Even there I think sometimes the railroadiness is a product of how the medium needs to be structured and packaged. I've had plenty of modules that offer up an overview of likely course of events, and it is easy to read that, and think these events are supposed to happen in this order, in this way, and it is the GMs job to make sure they do so. But if you examine the text more closely it is obvious this is just one way, the most likely way, that the adventure could play out, but the GM is expected to be flexible land adapt more to choices the players make.
Speaking of hook railroads, I think there are also certain types of adventures where you almost have to have some railroad to get to them. Or at least where I think the buy in makes it justifiable. This is possibly where I would defend railroad as okay as long as the players know and are buying into it. When I run monster of the week campaigns, this is how I tend to do things. There is an adventure. The players will go to the Temple of the Phoenix Spirit, or they will end up facing the werewolf of Moondale; but once there the structure is very non-railroad. Once the adventure starts, they can approach it however they want, I usually don't have a set list of things that have to happen in any particular order, and they can engage or disengage as much as they want (running away and escaping with their lives is a perfectly fine ending to the adventure). You could argue this isn't railroad because the players are buying in (but the structure does mean they are being railroaded into each adventure effectively).