I’m not sure the oath really worked, because people who were inclined to practice modernism weren’t concerned about lying in a sworn oath anyway. However, it did at least state that the Church was opposed to these ideas.
I am old enough to have known some members of the older generation (that is, priests who were already priests at the time of Vatican II), and I think dissent was unfortunately pretty widespread already, oath or no. Maybe they had to be quieter about it and a little more sneaky, but things wouldn’t have collapsed so fast after Vatican II if they hadn’t been weak before that.
I think people have never considered the effect that the American church had on Vatican II. Many of the supposed “problems” brought up at Vatican II were just an expression of the usual American Catholic desire to remove identifiably Catholic practices in order to fit in and prove that they were just as American as any good Protestant or non-believer. So modernization - and I’m not saying there weren’t certain things that did need a bit of an updating or refreshing - came to mean shedding anything that was identifiably Catholic.
This harmonized very well with the goals of leftists such as Bugnini, and I think gave them the power they needed to push their agenda through before the other bishops even fully processed what was happening. But that was, again, because the leftists were indeed Modernists, and their quiet, murmured heresy had actually been tolerated for a long time in the Church, oath or now.
What this article omits is that the Cultural Revolution of 1968 was pretty much civilization wide, not just American.
There were riots in Paris, and Charles de Gaulle fled to his country estate until things calmed down.
There were riots and terrorism in Germany and Italy.
The anti-war protestors and hippies in America had their counterparts all over Europe and the West.
Riots, burnings, barricades, revolutionaries throwing cobblestones in the cities of Europe—it was widespread.
And the fallout in Europe after Vatican II was as bad as it was in America, if not worse. The bishops over there are still more dissident or weak than they are in this country, even after decades of failing to fix the problem.
Ireland stood fast for a while, but now they seem to be as troubled as anywhere else.
The Church has gone through major troubles in the past, but this certainly has been one of the worst and most widespread.