Much like GMs I prefer to have GMs focus on situation instead of deciding how things should go before hand I have a fairly strong preference for players to focus on situation over story when it comes to defining who their characters are. I feel like railroading only enters the picture when people have strong expectations for how things should go.
The contrast between
situation and
how things should go is not always clear-cut, in at least the following sense: if a particular situation is going to arise
in the future then,
in the present, that sets a constraint on
how things should go.
Here's an example from the Burning Wheel Revised Character Burner (p 34) that shows what I mean:
Instincts are the most primal, compact way of telling everybody at the table what your character is about. . . . If my Dwarf has the Instinct, "If there's a cave-in, I push the youngest to safety," that tells the entire group a lot about who my character is and what he values. First, he's careful and aware of the dangers that come with being underground. Second, his first thought is to protect someone else, not himself. And third, that someone else is the "youngest" - meaning that he puts some sort of value in youth. . . .
Finally, there's the story level. On this level, an Instinct is a direct statement to the GM, "I want to showcase this aspect of my character." If I have the cave-in Instinct, I'm telling the GM that I want at least some of the game to happen underground in caves or tunnels, and I want to have a cave-in.
D&D doesn't use an Instincts mechanic, but in 5e at least there are elements of PC build that play a similar sort of role. In choosing a Bond, Flaw or Ideal a player might send a direct statement to the GM about what s/he wants in the game. The same thing might be done by choosing a particular background.
My reading of this thread, and my sense of D&D play more broadly, is that a lot of D&D GMs aren't happy with the idea that a player - via PC build - might impose these sorts of constraints on the fiction that the GM establishes in playing the game. I assume that's where this notion of "railroading the DM" comes from.