Was Vatican II a mistake?
We should judge a tree by its fruits. Don't you think Vatican II was a mistake? After all, look at all the nonsense going on today as a result of it.
Not everything that happens in the name of Vatican II is the fruit of the council, anymore than everything done in the name of Christ is the fruit of his teaching or of Christianity in general.
Are there abuses and violations of Catholic belief and practice today? Sure, but that means we should redouble our efforts to implement the teachings of the council, not disregard them ourselves.