Okay, I'm going to go through a list, and you tell me at what point in the list the GM is considered to be railroading.
1: GM starts a campaign in a mish mash world where anything goes and lets you do whatever you want.
2: GM starts a world with a defined setting (Fantasy, scifi, historical) and lets you do what you want within the parameters of that setting.
3: GM starts a campaign with a defined setting and gives your characters some overarching goal (like slaying the lich), but you can get there however you want
4: GM starts a campaign with a defined setting and gives your characters some overarching goal, you can get there however you want, but your characters are limited in that they must be part of some specific organisation, or have some specific motives for wanting to achieve the goal
5: GM starts a campaign in defined setting with overarching goal, your characters must come from some specific organisation or have a specific motive, and there is a fixed sequence of events that will deliver you to your final goal, deviation is limited to sidequests
6: As above, but no side quests
7: As above, but you are ferried from combat encounter to combat encounter, social situations are essentially played out in cutscenes
8: As above, but you can't even choose how to approach combat, you are frequently ambushed or are ambushers completely at the GMs discretion
9: As above, but you now have limited control even in combat, you are told outright what actions are acceptable and what aren't, dice are fudged constantly, and the big boss can't even be defeated legitimately until he has his cool cutscene moment
10: The GM reads you a book about adventurers slaying a lich