But if all that is required to be saved is faith, why would Catholics go to hell?
That is to say, if a person believes in Christ, why would he go to hell if he believed something else was required on top of that belief? He still believes in Christ, even though he might hold some extraneous beliefs.
If you don't understand Christ rightly, you don't know him at all.
And, those extra beliefs exalt man in the place of Christ.
Therefore, it would lead to damnation.