Hi BOS,
Well, I too, am a member of a baptist fellowship and don't consider that line of organization to be a part of what was initially intended as the 'protestant' fellowships. Therefore, you can take my answers for what they are worth.
I do protest against what the catholic organization teaches as the truth of God. Several have been listed and so this list will probably be repetitive in some of what is included here.
Indulgences: It is my understanding that from my own studies of the Scriptures that there is no such things as a plenary or temporal forgiveness of sin through any means other than simple faith in Christ, and with that, the asking of forgiveness from the One to whom we have sinned...God.
Transubstantiation: It is my understanding that the purpose of the communion is to be a time of remembrance and the bread and cup are merely instruments through which we are drawn to remember that our Lord gave up his flesh and his blood for me.
Veneration of Mary: It is my understanding that Mary was a woman, a sinner just like the rest of us, who was blessed to be chosen of God to be the vessel through whom His Son would be brought forth to the earth. Just as God chose Daniel and the many other prophets to do their part in completing His great work.
Infant baptism: No one can make another born again. Just as Jesus said, baptism must be coupled with belief. Any baptism where the one being baptized does not have a cognitive understanding of who Jesus is, in my understanding, is not a valid baptism.
Prayers for the dead: The dead are dead. Their final disposition on the day of God's judgment has been set. Just as with baptism, where the person being baptized must themselves have a knowledge of the Lord and willingness to believe, so to, must prayers for ones salvation come from the individual seeking God's salvation. I can pray and pray and pray that a loved one of mine might come to know the truth and find God's salvation, but ultimately the person being prayed for must accept that truth and seek after God's salvation for themselves.
Celibacy of the priesthood: While Paul said that it is good for a man, if he can, to not be married, the responsibility of one's being married is up to the individual person. Further, there is no indication in the Scriptures that any teacher need be unmarried. In fact, Paul makes it clear that they can, but that they must be pure in their marriage. He even gives an example that a man with a failed marriage or family won't be able to be head of any fellowship by telling us that if such a man can't control his own family, he certainly won't be able to control any part of God's.
Special dress of the heads of the fellowship: I'm absolutely confident that Paul, Peter, et.al., didn't put on some fancy outfit to stand before the body of God's people to teach them. There is absolutely no Scriptural justification that special clothes make anyone special to God under the new covenant. Paul didn't wear the priestly garb of the old covenant temple to preach or lead the early church. Neither did anyone else.
Purgatory: There is no condemnation or 'working off' of earthly sins for those who die as born again believers in the Lord, Jesus.
Annulment of marriage: I'm not even going to get into all the evil and wickedness that this single doctrine manifests.
These are just a few of the several dozen 'catholic church' doctrines that I protest of the catholic organization. All I can say is that I do know that one day, we will all know the truth. We will know who are those who have been deceived and who are those who have made themselves worthy to receive God's great gift of eternal life.
God bless you.
In Christ, Ted