The problem is that "railroading" really means "constraining player choice, but with a perogative connotation."That's why I think this definition is either way too broad...or railroading is a proper DMing technique.
At times constraining player choice is necessary or inevitable, and sometimes both. This should be obvious to anyone. The difficulty is that the attachment of a perogative connotation makes discussing it really tough.
Lets say we've got a word, "Blargle." And it means, including connotation, "Shrumpkins, but bad." If someone asks, "Can Blargle ever be good?" the obvious answer is No. Its got "but bad" right in its definition! Of course it can't be good. But the discussion really shouldn't be about Blargle, it should be about Shrumpkins. And the negative connotation attached to Blargle doesn't automatically apply to Shrumpkins. It might, and in some cases obviously it does, or there wouldn't be an entire word for "Shrumpkins, but bad." But the "but bad" doesn't necessarily apply in all contexts.