Since I know of the Roman Catholic church, and have not joined it, does that count as rejecting it knowingly?
I was under the impression that Luther's "invisible Church" was his excuse for saying that the Catholic Church as a visible entity was no longer necessary and one thus has the option of leaving. I don't believe I said anything to that effect. Nor did I say that a Protestant denomination is a "church" in of itself. In other words, Protestants come to God through the One Church, whether they realize it or not, and not through a church that teaches falsely.
As to your knowledge of the Roman Catholic Church, I cannot say how much you REALLY know. It is one thing to "know" it as information that you have heard but don't take seriously, and quite another to "know" the arguments of the Church's existence, take them seriously, and yet continue to reject them. "He who hears you hears Me and he who rejects you rejects Me and the One Who sent Me." I cannot make the judgment on "how much" you "know" regarding the Catholic Church as the Church of Christ. That is between God and yourself - for you will have to answer to Him based on your own personal knowledge on why you chose to avoid the Church He established - considering that God desires men to come to the knowledge of the Truth.
Regards