I've only come up with railroading in player RP'ing once and after a long and boring conversation, I realised that some people do like to have a predetermined idea of what should happen.
My partner calls it NPD, I call it bad RP.
I agree with you in that my default mode of RP and what I enjoy most is not having an idea of where we'll end up to.
However, I'd have to say that not all RP where there is a desired outcome explicitly put out is bad. Sometimes you manage to play yourself into a corner and need to have something happen to get you out of it, and in those cases I think figuring out what would need to happen for your character or her situation to change in a way that made playing enjoyable again, and then purposefully playing towards that, is quite fine.
I strongly prefer people with such purposes to share them with me beforehand, though, and ask me to co-operate in steering the story, rather than hitting me on the head with rails.