Due to the variety of versions of the Protestant faith, I cannot claim to represent them all. I am an evangelical reformed Protestant (try saying that 12 times really fast!) and even there I am mostly representative of myself. So, I make no claims to represent anyone reading this!
I will describe my past views of Catholicism in places here. Many of them are inaccurate. Read through to the end, please, brothers and sisters, before you correct me!
In the beginning…
I thought it would be most useful to organize my perspective chronologically rather than thematically. My first encounters with Catholics were a disaster. I attended Catholic high school because there were no Protestant Christian high schools close enough to suit me, and while there are many good teachers and some of my teachers knew their faith well, the first ones (and the ones I had most frequently) were not. My teachers taught me (in no particular order) that the Bible was entirely myth except the Gospel (or maybe just a random sampling of books were myth, according to others,) that Jesus was sinful and that all religions are equal paths to salvation. Most of my teachers were clueless when it came to the Bible and I quickly became very arrogant and confident in my Biblical knowledge.
This was, you must remember, on top of the traditional Protestant dislikes of Catholicism: the idolatrous devotion to Mary, weird ideas about the Lord’s Supper and slavish devotion to the Pope. I quickly became convinced that Catholics were unbiblical heretics, at least seriously misguided, quite possibly doomed to hell.
Still, I had a couple of incidents that caused me to reflect on my position.
I was rather outspoken, and when I wrote a particularly nasty response to some questions on Catholicism, my teacher offered to talk with me. This was at the end of the year, and I spent too much time reflecting on whether or not to take him up on his offer that the moment passed. I was sufficiently ashamed (I really liked the teacher, and my response was not charitable at all) that as a self-imposed penance I went to Reconciliation at school. I awkwardly entered the room with the priest, told him I wasn’t a Catholic and didn’t agree with the theology behind reconciliation and penances etc, but that I had not been very loving in the way I interacted with Catholics and would appreciate some prayer. I was impressed that he simply prayed with me.
When my Grade 11 teacher told me that all religions were equal paths to salvation, I actually argued against her position using an appeal to both the Bible and Catholic beliefs. I knew enough about Catholicism to know that she misunderstood the faith she claimed to have.
In Grade 12, a teacher who was not teaching my class heard me asking questions to a visiting priest and invited me to speak with him at lunch. He was a theologian, and clearly knew the Bible well. We only had a chance to talk briefly, and what I most remember was his great sadness after I recounted the things I had learned, and he said that he really hoped that my experiences had not damaged my faith.