If you insist. impugn: to challenge as false...; cast doubt upon. (https://www.dictionary.com/browse/impugned)
On the one hand, as an Evangelical Protestant, I had firm convictions about the finished work of Jesus Christ;... But the application of that redemptive work of Christ by the Holy Spirit is another matter, one that I did not really come to grips with...Now that block, that obstacle was one of the biggest...
Implication: Protestantism, specifically evangelicalism, was deficient in what it taught, thus imputing fault, casting doubt upon the same, impugning that faith in contrast to Roman Catholicism. And which premise the rest of his deficient, faulty, ignorant, Scripture-wresting , sophistical apologetic follows (which I am tempted to show point by by point, but that would take even more hours with my stiff arthritic finger). Thus his apologetic is an an argument against being a Catholic.
"Just being a convert from it itself impugns whatever is under that big tent." "That an unnecessary hateful statement against this man."
"hateful statement? I was simply stating a fact.
"What right do you have to pass judgement on him. "
What right? Did you ever read "have no fellowship with the unfruitful works of darkness, but rather reprove them." (Ephesians 5:11)
" Aren't YOU a convert as well - does that not apply to you..?"
Indeed, and thus being a convert from Rome itself impugns that big tent.
"You should for sure be proud of your bible learning, no doubt... but be careful how you use it-- ANYONE of us can fall into the trap...as C.S. Lewis cautions: “That raises a terrible question. How is it that people who are quite obviously eaten up with Pride can say they believe in God and appear to themselves very religious? I am afraid it means they are worshiping an imaginary God.” ― C.S. Lewis, Mere Christianity "
So now your recourse is to impute sinful pride? Well, that is par for the course, and this exchange itself is an argument against being a Catholic. Been there myself. May God peradventure grant you "repentance to the acknowledging of the truth." (2 Timothy 2:25)