I don't think it is de fide because so many Catholics don't believe it and believe instead that there are many upright pagans who do not commit mortal sin and are in the state of grace and will be saved without the sacraments.
Hahahhaha, lol.
Yep, that's the bane of our age unfortunately. But we know it isn't true because all the fathers and saints unanimously held the overwhelming majority of men are damned, unfortunately.
'How many among these uncivilized peoples do not yet know God, and are sunk in the darkest idolatry, superstition and ignorance! . . . Poor souls! These are they in whom Christ saw, in all the horror of His imminent Passion, the uselessness of His agony for so many souls!'
St. Francesca Saverio Cabrini
http://saintsquotes.net/Selection%20-%20Fewness.html