Now, sincerity can enter in to a point, such as when you "sincerely" THINK that the Church taught something but were wrong.  That's the nature of material heresy, where you believe the wrong thing but for the right reasons.  St. Augustine says that the litmus test for identifying this type of heretic is their readiness to accept correction.  When you explain to them that, "oh, that's not what the Church teaches", they'll immediately respond with, "oh, wow, sorry ... did not know that" and then immediately change their minds. 

This describes my situation regarding a central Christological dogma (I'm assuming that's the word).  Until two or three years ago, I thought that Christ had always had both a divine and a human nature from the instant of His begetting, but that the human nature was just held in abeyance, latent or dormant if you will, until the moment He became incarnate, kind of the way that any of us have a human nature even after we die, but our souls are separated from our bodies (or what's left of them) awaiting the resurrection.  I did not realize that His human nature didn't exist until the Incarnation.  I probably never read that anywhere, I just inferred it from what we know about the hypostatic union.  When I did read it, from some traditional source (I think it was the Baltimore Catechism when I was teaching my son in homeschool religion class), I said to myself "oops!" and immediately adopted the true, orthodox teaching.  And, no, I didn't make some kind of "abjuration of error" after the fashion of Richard Ibranyi ("RJMI").  Recognizing my error and fixing it in my own mind was quite sufficient.

So I suppose you could say that, up to that point, I had been a material heretic in the fashion you describe, but definitely not a formal one, because I truly believed that this was what the Church teaches.

How true.  Many Protestants, as well as those who grow up in a Protestant culture but are not baptized and do not receive formal religious instruction, have a vague, gauzy concept of "God, Jesus, and the Bible" and cobble together a hodgepodge of personally agreeable ideas that make sense to them, and give it no thought any deeper than that.  If they have been baptized as infants into one of the mainstream Protestant sects (Anglican, Lutheran, Methodist, Presbyterian, and so on), many of them couldn't tell you the first thing about the history of their denomination, and certainly couldn't tell you anything about the period between "the early Church" and the 1500s.  The most they might know is something like "Luther was a good guy" [sic].  Their awareness of religion is pretty much limited to what they've seen and heard in their own lifetime.

Long story short, Protestants are not ten feet tall.  They're highly suggestible to whatever they're told that "sounds right" to them.  I grew up in such an environment, and I can tell you what they're going to say before they ever even open their mouths.  It's not terribly deep stuff.

So, as I've said before, the degree of culpability does not matter in case where someone is simply lacking the correct rule of faith, since without that rule of faith, one cannot have supernatural faith, and whatever one does believe, he does not believe it with the true and infallible supernatural motive.  One does no thave to actively reject the faith in order not to have the faith.  Animists growing up in the jungles of African do not have the faith, even if they've never heard of it, and therefore have not rejected it.  Cradle Protestants are in the same category, although most are not considered infidels like the Animists.  They're in the same category in terms of lacking the faith without having actively rejected it (due to inculpable ignorance).

What I meant is if you NEVER had the $100, NEVER even heard of $$$. Or are you saying all are born with innate knowledge that faith exists, and know innately that there is correct and incorrect faith?

You're mixing up the notion of "current knowledge of the faith" vs "final knowledge, on deathbed, before they die".

When the Church says that protestants are heretics, who are GUILTY of not having the Faith, this is a true statement.  It is dogma.  We're talking about their current status, today, as a protestant.  

What you are adding to the equation is the notion of "what if they have never heard of the Faith?".  For protestants, this is nearly impossible, because
1) most are baptized, which means they have the supernatural virtues of faith, hope and charity (in seed form, in their souls).
2) most protestants preach CONSTANTLY about catholicism, and how it's wrong.  Protestants really don't have a faith, they just have a "not a catholic" faith.

Even if there was some sincere protestant out there, then we say that INFALLIBLY that God will give them the knowledge of the Faith (at some point before they die).  Then they will be fully guilty, if they reject it.

But even before this opportunity arises to learn of the Faith, they are still correctly called heretics.

This is totally backwards.  The protestant doesn't know/care that the Church is the proximate rule of Faith because they ALSO reject the Church's authority.  They are formal heretics, without a doubt.

Protestants are heretics simply in law.  However, they are not necessarily formal heretics (i.e., guilty of the sin) before God.

Protestants are heretics simply in law.  However, they are not necessarily formal heretics (i.e., guilty of the sin) before God.

Wrong.  If we're talking about baptized protestants, that means they have the virtues of faith, hope and charity, due to the sacrament.  If they reject such graces (which the unbaptized do not get), and they continue on in their errors, they are guilty.  There are MULTIPLE ways which (as St Thomas explains) one can be guilty for ignorance and having a poorly-formed conscience.  Ignorance will damn a person to hell.  Because ignorance means that person didn't search for truth, didn't pray enough, didn't follow the graces they were given.  Protestants who continue on into protestantism in adulthood, are guilty.

Wrong.  If we're talking about baptized protestants, that means they have the virtues of faith, hope and charity, due to the sacrament.  If they reject such graces (which the unbaptized do not get), and they continue on in their errors, they are guilty.  There are MULTIPLE ways which (as St Thomas explains) one can be guilty for ignorance and having a poorly-formed conscience.  Ignorance will damn a person to hell.  Because ignorance means that person didn't search for truth, didn't pray enough, didn't follow the graces they were given.  Protestants who continue on into protestantism in adulthood, are guilty.

Ignorance does not equate to pertinacity in regards to heresy.

What are you trying to point out here in response to my post?

You said Prots "are not necessarily formal heretics (i.e., guilty of the sin) before God."

But that goes against the warning of Our Lord in the Scripture I quoted, which is what I was pointing out.