More major sins that Roman Catholics are taught to practice:

Prayer for the dead

To begin, lets look at a word from the old testament that was about an Abomination.
NECROMANCER
That word ,in the hebrew ,means; seeking and asking with the deceased.
One common error in defence of Catholic error, is to say that it is ok because they were once our saved brothers on earth. Well, look at the time that the prophet Samuel was called on after his death; That was an obvious sin against God. Just because something is real and it works, doesn't mean it isnt a sin against God.
Praying to the dead is a form of Necromancing, and it is an abomination to God.

This includes all prayer to any being in heaven except to God Himself. The old testament is loaded with examples of sins where people worshipped all the hosts of heaven.
It is strictly written: God only shalt thou worship.
Roman catholics try to cover up the fact that they practice idolatry, by calling it ,veneration; And try to get around idols by calling them icons. If God says Dont carve or mold any likeness of things in heaven or on earth, He means it, no matter What you call it, or what you claim you use it for.
To the pure, all things are pure, but if we do willingly ignor and disobey Gods commands, are we pure? When Jesus became our high preist he changed some parts of the law, but these commands have never been mentioned to have been changed; On the contrary, we are reminded several times in the new covenant to keep ourselves from idols! The command about idols was not at any point changed.
One reason Catholics want to pray to the dead is because of the Catholic doctrine of "purgatory"
Now, there is scripture reffering to a place of tourment that isn't hell, and a place where some fallen angels are held in chains, and the outer darknes, a place of tourment; but none of these descriptions tell us that there is any effect a living christian on earth has anything to do with interceeding for them. If there is a place one must go, apart from heaven, to receive stripes, it is not instructed to us at any point to pray for their early release.
If God sends someone to a place like that to receive payment for unresolved sins, that person just needs to pay up however long the eternal judge committed, if it be so, that such a place is purgatory. Besides that, It is written, He is faithful and just to forgive our sins and to cleanse us from All unrighteousness. If it were a matter of sin, gods forgivness covered that.
It's not very enlightened to try to copy the erring ways of an unsaved people from a book that wasn't included in the bible. Those people who catholics try to justify prayer for the dead about, who paid offerings to the dead, from an un canonized book; It is no more Gods instructions than are any of Job's false accusations against God. Job was a just man of faith who said many things we know are not true. Job didnt have the book of Job to go by, but we do. We know it was the devil who took away, not God; at least in his case.
It takes a true Apostle of God to see Spiritually enough through the muddled mess of deception that has gathered over the past two thousand years, from a long line of humanly chosen leaders in the roman catholic church. When people are given to heed tradition, instead of only studying Gods Holy Bible, then the darkness of deception clouds the eyes of understanding. Anybody, even a devout practicing roman catholic, who is humble enough to admit they might be wrong, and examine the bible long enough, not trying to defend an old tradition, but truely wanting the Holy Spirit to lead into all truth as they read and study the bible; They should be able to recover themself from deception into the real truth.

Remember; Mary said to do what Jesus said. Jesus said to pray directly to Father God.
Anything less wont get it, and anything more is forbidden.
God is a HOLY God , and God is a jealous God.
Dont get caught up in disobeying Jesus by coming up some other way.
The more you study the errors of roman catholic doctrine, the more you find that it robs God or Jesus from the rightful positions only they are supposed to have, and it robs you of your rightful authority you have in him.
The theif cometh not, but to steal, and to kill, and to destroy.
Jesus said in John 8:34 "whosoever committeth sin is the servant of sin"
"sin" means missing the mark. We do not want to be sitting back trying to defend what we are deceived about, we, who want to say we love the truth, want to examine ourselves to see that we be in the faith. Deception is a form of unholiness. We need to be striving and seeking and hoping for more holiness, to come more and more like his holiness; Without being this way, allowing Gods Spirit to develop this attitude in you; You will not see the Lord. Hope for truth and long for it to be evident in your life; The love of truth in searching to be at peace with others and hoping for Gods holiness in your life.

Some of the most powerful strongholds of sin are false doctrine; human pride locks us into them, Spirit led humility will lead us out. Then you can read John 20:23 to yourself.
Amos 3:3 says "Can two walk together , except they be agreed?" The same power of deception is the same power of being free from deception; It depends on who you agree with. If you agree with those who have a Spirit of Lies, and have received strong delusion, you will partake with them in their blind attitude and reward; If you can hear what saith the Lord about what is true, and walk in it, you shall be free.
Did you know that every catholic church keeps a human bone at it's altar? They call it a "relic" There are some very strange things that go on inside the roman catholic church. Where do you want to put your faith, in human remians, or in the word and Spirit of God?
In Proverbs 8:36 Where the wisdom of God is speaking, it says "But he that sinneth against me wrongeth his own soul: all they that hate me love death."

Does having a need for human bones in your church sound like those who love death? Sounds kind of creepy to me.
Let God be your Lord; listen to what others have to say, but dont let them control what you are going to believe and do. I sincerly pray that my work here helps you in your walk with God.
Throughout history, there had been some Roman Catholic leaders who were devoted iconoclasts; Who seemed to have been onto the right path, destroying the massive idols and rightly calling them so; But there was a strong resistance who came up with very clever disguises for the truth. Those kind of people are not true lovers of truth; the ones who stopped the iconoclasts and covered up the truth about idols.
The old testament is loaded with people who hid or covered idols. God sees everything, even the hidden thoughts of your mind.
These days, Look at what has become of roman catholic love of truth; The buildings all around the vatican city have huge statues of saints atop the roofs of the buildings. Right smack dab in the center of the court of the vatican is the largest oblisk, transported from Egypt; It is believed to house the sun God. This whole matter is so full of trouble it could almost explode in your face as you see how much energy is devoted to the lies.
Do you think there is nothing they wont do to defend their "Tradition"? Remember, a tree is known by it's fruit, by whom or what do you abide?