Allow me to give a thesis then.
On one hand, you have NCR as heroes. The NCR is one of the few stabilizing forces for civilization in the Wasteland. How good are they at their job? The Brotherhood of Steel went ALL OUT against them in their own backyard and eventually got their butt handed to them. NCR began as a Vault-based society and they managed to turn the freakish social experiment into something that actually has the potential to rebuild humanity.
It's a liberal democracy that wants to rebuild the Old United States. It has a constitution similar to the Old World United States. Heck, it even has railroad technology - the first sign that the United States may eventually be able to be crossed by people. There's also a nice bit of "do not **** on the bear" with the fact that NCR isn't remotely a wimp.
If you mess with NCR - Brotherhood of Steel or Great Khans, they will throw you down.
OTOH...
NCR is also a force that doesn't really seem to honestly CARE that much about the people it attempts to bring under their wing. They seem to assume everyone SHOULD be a part of NCR and if you're not part of NCR you're either an ignorant tribal that needs to be "re-educated" or you're just an enemy who needs to be wiped off the face of the Earth. They actively try to colonize New Vegas so they can justify their takeover and start forced settlements despite the fact that the Mojave is already inhabited.
Hell, it's obvious they actually hold the inhabitants of the Mojave in outright CONTEMPT - their soldiers frequently deriding them and saying they shouldn't have known to mess with them. Mister House may be a tyrant but he's right that NCR has no claim to either Vegas OR Hoover Dam (which Mister House brought online). The Brotherhood of Steel did the same with Helios One, only for NCR to attack them and seize it.
If the prewar US is the idealized, gilded-over hell of the 1950's McCarthy "world of tomorrow," then the NCR is a sort of high-tech Age of Expansion US (mid-late 1800's.) The drive to be coast-to-coast, manifest destiny, and all that came with it. That US was a very double-edged sword, as it brought economic security, a powerful Army, a set code of laws and reasonable and fair trade. However, they tended to either crush or absorb everyone they came into contact with (ie: the Native Americans.) A great many very good things were done in that age, and an equal number of outright vile ones as well.
Every nation is like that, even today.
The failing of the NCR is in presentation vis-a-vis it's enemies, rather than it's own. It's a morally gray if well meaning power going up against and outright black-and-white evil enemy (the Legion.) It's a believable middleground nation going against an almost comically evil one, and the extreme disparity is what generates so many blind fans for the Legion. The NCR's face is pretty bland until the player digs deeper, while the Legion starts throwing grimdark around like it hasn't gone out of style already.
It's also why the extremes of Encalve and CW BoS love/hate exist.
All that said, I'd still call the NCR heroes. Why? Because unlike Caesar, the BoS, Mr.House or the Yes Man, the NCR is actually
striving for something grand that can better the lives of every man, woman and child under it's
wing furry paws. They know they've got problems, but forge ahead anyway knowing full well that the odds of pulling off their gmabit are very long. The risk is extreme beyond belief, but the rewards are equal.
Meanwhile Caesar wants to paint the Mojave red to fulfill his insane monomaniacal fnatasy, House just wants to keep his power to himself, and Yes Man is pretty much a status-quo fart in the wind.
And, finally, I'll say again;
Bitter Springs is not good evidence of the NCR being "evil." It's a chilling example of what happens when military communications break down in the middle of an operation, which can, has and WILL happen to every military to exist. Neither side is at fault.