Could it be that the loss of formality associated with the cultural upheavals of the mid-20th century is not due not to the ideology of egalitarianism, but rather may the triumph of one culture over another in some areas? That is to say, while some of the loss of manners can be explained through the neglect or deliberate rejection by certain people, could it be that not all traditional American cultures possessed the same set of manners? And as groups bearing a more informal culture migrated westward and become dominant, they had a lasting impact on the culture of various regions?

I am thinking specifically of Scots-Irish culture, but I do not know enough about traditional Scots-Irish culture to make the claim. Would it be correct to say that traditional Scots-Irish culture is more casual or informal in comparison with other traditional Anglo-American cultures, with which awareness of social hierarchy and more "aristocratic" manners/etiquette are associated? I have heard that the Scots-Irish were more independent-minded and suspicious of government and the traditional Anglo elites.

Or might it be the case that traditional Scots-Irish culture, though being more informal, nonetheless recognized some social differences, or borrowed this from another culture?

How about the attitude that someone else must earn my respect before I give it to him? Is this something to be found in traditional Scots-Irish culture? It does seem to be an attitude of some Americans.

I'm satisfied with an explanation that discusses the loss of confidence or satisfaction in traditional American mores, but I am open to the possibility that something else was at work in addition to this.

I haven't read Jim Webb's book on the Scots-Irish, but here is a short piece he wrote for the WSJ. Something relevant?

The Scots-Irish are derived from a mass migration from Northern Ireland in the 1700s, when the Calvinist "Ulster Scots" decided they'd had enough of fighting Anglican England's battles against Irish Catholics. One group settled initially in New Hampshire, spilling over into modern-day Vermont and Maine. The overwhelming majority -- 95% -- migrated to the Appalachians in a series of frontier communities that stretched from Pennsylvania to northern Alabama and Georgia. They eventually became the dominant culture of the South and much of the Midwest.

True American-style democracy had its origins in this culture. Its values emanated from the Scottish Kirk, which had thrown out the top-down hierarchy of the Catholic Church and replaced it with governing councils made up of ordinary citizens. This mix of fundamentalist religion and social populism grew from a people who for 16 centuries had been tested through constant rebellions against centralized authority. The Scots who headed into the feuds of 17th-century Ulster, and then into the backlands of the American frontier, hardened further into a radicalism that proclaimed that no man had a duty to obey a government if its edicts violated his moral conscience.

Matched with this rebelliousness was a network of extended family "clans," still evident among the Scots-Irish, built on an egalitarianism that measured a person by their own code of honor, courage, loyalty and audacious leadership. Noted Scottish professor T.C. Smout said it best when he observed that these relationships were "compounded both of egalitarian and patriarchal features, full of respect for birth while being free from humility." They demanded strong leaders, but would never tolerate one who considered himself above his fellows. Andrew Jackson, the first president of Scots-Irish descent, forever changed the style of American politics, creating a movement that even today is characterized as Jacksonian democracy.