So Americanism is just ignoring/disobeying certain parts of official Church teaching based on personal preferences and motivated by a mistaken idea of liberty? Americanism can be any heresy as long as it is professed to be motivated by liberty?
Freegards
I think one of the difficulties in defining or combatting heresy was the point you just made, “Americanism can be any heresy.” Most heresies have a leader (the heresiarch) and a formulated statement, but Americanism was more a tendency than anything else, and hence very difficult to either identify or combat.
Some people, such as Isaac Hecker, founder of the Paulists, were unfairly tagged “Americanists” simply for wanting to do things that they thought would bring the Gospel to Americans in a way that standard European approaches could not. The Paulists were very devoted to street preaching, for example. Once upon a time, Catholic preachers had roamed Europe, but in 19th century European Catholicism, this was unheard of.
So I would say yes, that if you had to define the essence of Americanism, it is a belief in some sort of totally unbound, unattached “individual conscience” that is free to decide upon moral laws depending on whether the individual finds the following of those laws to be to his taste and convenience or not. Americanism is much less a theological heresy, such as Arianism, for example, or some heresy dealing with the Trinity, and instead is a sort of “practical heresy” relating to the moral field. But it is still difficult to define because it has no leading proponent. (Of course, nowadays, after Vatican II, which in some ways paved the way for the full flowering of Americanism throughout the Church, it’s probably harder to find someone who ISN’T an Americanist!)