As a life-long Protestant (soon to be received into the Church!) I can give you my perspective.
First, the church I grew up in was full of ex-Catholics, including my parents. They would say things like, “I never knew Jesus when I was a Catholic.” So I grew up in that atmosphere. I never hated Catholics, but I felt sorry for them. I could see how all their beautiful rituals could make them think they were religious, but if they didn’t know Jesus the rituals were empty. My Catholic relatives didn’t help matters, because all of the Protestants I knew were passionate and outspoken about their faith, and the Catholics didn’t want to talk about it… and in many cases they had major sin issues, too. It is just a matter of what you see growing up. I mean, when a Protestant relative is telling you that God delivered him from alcoholism (and there’s proof!) and your Catholic relative is getting bailed out of jail for knocking his wife around when he was drunk, what does that tell you as a kid?
I was married with four children before I met a Catholic that lived her faith, and I live in a largely Catholic area. My great-grandmothers were Catholic women of great faith, but that was “way back then.” When I met someone my age, living the Faith NOW, it rocked my world. That was about five years ago and is what started me on the faith journey I am on now.
There are “theological” types who have all kinds of “Biblical” evidence that the Catholic church is the whore of Babylon. If you read what they’re written and don’t have a lot of experience reading the Bible, it is easy to get sucked into what they say. It is sad. However, the book of Revelation (the Apocalypse) tells us which “great city” is the whore and it is the city where Our Lord was crucified (Jerusalem).
There is also the matter of being saved by “faith alone.” My mother-in-law, who is a pastor’s wife, told me that a cult is any group that tells you you need anything besides faith in Jesus to be saved. If that is true, than Catholicism is the most successful cult of all time. Again, if you haven’t read the epistle of St. James lately, it is easy to get sucked into that way of thinking. However, St. James, and Jesus Himself, teach us that our faith must be accompanied by works and we are not saved by faith alone. End of story.
I could keep going but my kids want breakfast.

Hope this helps.