Well, as a DM who plans and occasionally had talks with my players about railroading, consider some of this from his point of view. Since he ain't here, I'll be him:
You guys go home every week and do nothing. You level at the end of a session, and when you come back next week, you haven't even bothered to make your new-level character, so we all have to wait for you. In short, your commitment to the game is so weak that you don't do any work out of game, while I have to slave away making monsters and calculating skill points and stuff. If I make a certain character or monster, you can be darn sure I'm using him.
You guys also don't really roleplay. You SAY you want to roleplay and that I never give you enough time, but you don't really roleplay whenever I give you the opportunity. What you really mean by "roleplay" is either "brood" or "joke about how tricked out I am in a specific skill or combat style". I offer you moral ambiguity, and you complain about being screwed no matter what you do. I offer you intrigue, and you whine about it being too hard. I make things more obvious, and you complain about being railroaded. Your characters have no personalities, so they have no goals, so if I didn't make plot hooks happen to you each week, you'd just sit there blankly like a Baldur's Gate character whose player has gone off to the kitchen and forgotten he was playing a game.
And when you do complain, there's a bunch of accusatory whining. More than half the time, the whine is a power-boost request disguised as a complaint. The ranger complains that he hasn't gotten to fight in the wilderness enough lately, and that I need to bring in more of his favored enemies, which he's never actually displayed any sign of hating when I did bring them in. The rogue whines that the sorcerer is too powerful, and that his abilities are always nerfed in combat. The sorcerer complains that he doesn't have enough skills to be an interesting character. The cleric complains that he's stuck being heals-on-wheels. In short, you're all playing your characters ineffectually not just as roleplayers but as powergamers, and then asking me to artificially make you more powerful to make up for it.
Why exactly should I throw away the story I've got? In the chances I've given you, you've shown NO SIGN EVER of being able to proactively do anything on your own.
Note: I don't know if any of that is true. I've got no clue whatsoever. But I do know that I'm only hearing one side of this complaint, and all the people attacking the DM have never seen the game in question. I've heard players call out "railroading" because they didn't like the in-game consequences of their potential actions -- but railroading should only apply to out-of-game dynamics between DM and Players, not between NPCs and PCs. A DM who has an evil wizard kidnap your PC's sister and demand that you go destroy some dungeon is not railroading you, unless he also arbitrarily says that you have NO CHANCE of using Scrying, Gather Information, Bribery, or some other method to try and rescue her instead of going into the dungeon.