A decidedly political movie, as well as decidedly creaky
If you can get past the B&W photography and the creakiness (it feels like a stagey movie from the 30s), the story is meaty with mindfood:
At its core it's a tale of fascism vs. democracy: the oppression of the strong thug over peaceable honest folk. They all despise Liberty Valance (Marvin), but they're curiously impotent against him and his gang, which actually doesn't reflect the real Old West where, generally speaking, regular citizens were tough, courageous people. A good example is the James-Younger gang, who were shot to ribbons in Northfield, Minnesota, when the townspeople got word that their bank was being robbed. Same thing happened to the Dalton Gang in Coffeyville Kansas. Both of these outlaw gangs were far larger than the 3 gunmen of "Liberty Vanlance." In any case, Doniphon (Wayne) could challenge Valance and does to some degree, but since Stoddard (Stewart) is his rival concerning Hallie's affections it would be counterproductive to go overboard in assisting the man.
This is a decidedly political movie as it focuses on the founding of towns, illustrating the myriad operations of government: The important parts a free press and community assemblies play, the deliberations concerning possible statehood and the powerful role of education in civilizing a settlement & purging the lawless breed.