I think you're right that seeing the U.S. as a unit plays a part. It was seen less that way at one time, but the idea was made concrete by force of arms in the Civil War. So, I think we think of people moving west over the ocean, then moving west over the land till they hit another ocean. Kind of all one gradual event playing out.
And you mention popular heroes of expansion. Unless I'm forgetting some things, I think we just don't have much in the way of heroes or events involved in the Westward expansion. I mean heroes like Davy Crockett and Daniel Boone arose during that time, but weren't really involved with the expansion. Maybe it was too gradual? Two exceptions are Lewis and Clark, who made the famous expedition. The other significant events I suppose would be the California Gold Rush, and the Mormons trying to start their own nation in Utah. I guess the way Oklahoma came to be is an interesting side note. They taught us about Lewis and Clark and the '49ers in school, they didn't tell us about the Mormons. Other than the whole expansion itself, there's not much specifically to protest. Of course things are moving fast and I wouldn't be surprised if I wake up tomorrow to find out they've banned reading about Lewis and Clark.
Oh wow, as soon as I finished that paragraph, I suddenly realized I didn't notice the water I'm swimming in - Texas. A revolution, and then a war, over a big chunk of real estate, and there were heroes, so that was a big deal. We're the only state of the 50 that requires its schoolkids to learn state history.
You've kind of opened the door for me to rant a little, and a rant goes good with coffee, so... I live where the Alamo is. The city is run by a city council which currently consists of approximately one conservative, and ten lunatic, wanna-be tyrants. In front of the Alamo there's a large stone cenotaph, a memorial to the heroes who fought and died inside the Alamo. My family name is on the cenotaph because an ancestor of mine died in the battle. Here's a pic so you can get an idea of the size of it:
The council is going to spend millions of taxpayer dollars to move the cenotaph. I'm sure they'd prefer to just outright destroy it, but they probably couldn't come up with a justification for that, so they're going to move it to some nearby side street where tourists won't see it, except for the few who may happen upon it. I imagine tourists of the future who do see it will wonder "why didn't they put this thing in front of the Alamo?"
This is part of a larger plan. Right now, there's a little plaza area in front of the Alamo. It's an open relaxed space where you can mill about, sit on a bench or on the grass and have a snack. Admission is free so you could wander in an out of the Alamo. For a fee, if you want, you can have a guided tour where someone tells the story. What the city's going to do is cordon off the area in way that forces persons to be corralled though an entry way where they'll be forced to listen to a guide, who's going to be telling a new story. They city says it wants to present a "broader view" of the battle and surrounding circumstances. There is no broader view. This isn't mysterious ancient history. We know everything there is to know about what happened, from both sides, at least sufficient for any questions a casual tourist or local child might have. I believe they may be attempting to create a new myth.
I haven't heard of a single resident of this city who isn't opposed to the whole idea, if nothing else for the unnecessary waste of money, but the politicians know what history is best for us, so they're barreling ahead with the plans.