from trad123's citation of St. Thomas.
Now it is manifest that he who adheres to the teaching of the Church, as to an infallible rule, assents to whatever the Church teaches; otherwise, if, of the things taught by the Church, he holds what he chooses to hold, and rejects what he chooses to reject, he no longer adheres to the teaching of the Church as to an infallible rule, but to his own will.
This is precisely what I was arguing against Drew, who basically called me an idiot for holding the same thing St. Thomas teaches ... and thereby implying the same of St. Thomas. I argued that if someone doesn't have the Church for a rule of faith, then the rule of faith reduces to his own private judgment (St. Thomas refers to it as "his own will".)
Such a one may be completely sincere, but if he doesn't have the infallible formal rule of faith (the teaching of the Church), then he doesn't have supernatural faith. If he's sincere, then God will not punish him for this. But lack of culpability does not supply for the lack of faith ... unless you're a Pelagian.