To be very clear: when i say "nobody believe that"... technically is the opposite 😉
Nobody that can actually think, knows history (the one that did not start with the last current thing... actual History), can see behind the curtains of obvious rhetorical talks...
Which technically is basically nobody. Most of the rest do not have the interest, the tools, access to information or, well, the will and reasoning capabilities.
So in a sense the "spreading democracy" narration / mission is a tool. In a sense it actually is what moves the US. It's made up? Yes. It's the deep real reason? No. Still it has impact or US would have not become what it is. No Empire can without an actual universal mission.