I think this issue reveals my deepest difference with the Catholic belief system.
Regardless of what any human says, my salvation is assured. Per the Word and the indwelling Holy Spirit. :-)
We don't believe in any "assured salvation," if by that you are arguing for an antinomian system. ("I can commit any sin I want to and go to heaven without repenting; I'm infallibly saved.")
Most "assured salvation" Protestants aren't antinomians, however. They say that someone who seems saved and then sins grievously and dies without repentance was never saved to begin with. That seems like a dodge to me; did they know they were never really saved at the time they were telling people that they were infallibly saved? If they did, then any "assurance" you think you have is sitting on sand, because they thought they had the same assurance.
In the end, it's really quite simple. "He who confesses me before men, I will confess before my heavenly Father. He who denies me before men, I will deny before my heavenly Father." (Mt 10:32-33) "Not everyone who says to Me, "Lord, Lord,' shall enter the kingdom of heaven, but he who does the will of My Father in heaven." (Mt 7:21)
Make sure your actions (not just your words) confess Christ and do not deny him before men.
You wrote:
"I think this issue reveals my deepest difference with the Catholic belief system. Regardless of what any human says, my salvation is assured. Per the Word and the indwelling Holy Spirit."
I guess that issue also reveals that you differ deeply from Paul who warned the Philippians (who had already accepted Christ and been baptized): "Work out your salvation in fear and trembling." (Phil 2:12)
Selective reading of scripture and personal interpretation thereof: short road to big errors! And not a problem in the "Catholic belief system"!