Hi LiamQ,
I have a really good point of my own I’d like to bring up to contribute to this discussion. As people here already pointed out, the Roman Catholic dogma and teachings surrounding Mary are sticking points.
I have before me a Catholic pamphlet labeled “Pray the Rosary Daily.” I open it up and come to a page that says “The Promises of Mary to those who pray the Rosary.” Promise #1 says “Whoever shall faithfully serve me by the recitation of the rosary, shall receive signal graces.”
As a Protestant, serving Mary in this context is perceived to be unbiblical because we can read that Jesus says to serve God only(Luke 4:8; Deut 6:13). We make sense of this conflict by concluding that Catholics have a man-made tradition that is not only unbiblical, it conflicts with the bible—Jesus’ command to serve God only—by having Mary ask catholics to serve her. How can a protestant who adheres to Sola Scriptura not perceive that as idolatry? Some even probably view this as unbiblical revelation by a deceiving spirit masquerading as Mary to lead catholic christians away from the one true God, or at least serve an idol/deceiving spirit alongside God. There is seen a precedent in Chronicals and 1 and 2Kings where Israel was led astray by idols and the same thing is perceived as happening again today.
Hope this helps provide more insight. I in no way am speaking on behalf of Protestants here.
This was a sticking point for me as a protestant for years—and still is. I’m still wrapping my head around this as I seek to convert to the Catholic Church.