As a ministry, Bible Brain takes special care to distinguish between a religion and those who follow it. Particularly in our culture, in which we tend to know more about our favorite TV shows than our religion's teachings, it's all too common for people to claim a specific religion while being more generally compatible with others. I find this very often as an apologist. I'll cite an official source, and someone will say "no, my religion doesn't teach that". Well, actually, it does, it's just you don't believe it.
This makes it particularly difficult to criticise pseudo-Christian religions. An error without criticism becomes twice as stubborn, but when people hear "that thing you believe isn't Christian", their mind automatically translates it to "you are not a Christian". In reality, no Christian is free from all error. We all sin, we all make mistakes, we all take certain things for granted, we all reject certain things out of hand. If anyone tells you they have perfect theology, theirs is the least perfect theology of all. Therefore, it is entirely possible, and I believe this is the case, that there are true Christians in every denomination, even the heretical ones. Nevertheless, there are heretical denominations, and true Christians should come out of them.
The prime example of this is Catholicism. While the Catholic Church claims to be the one true Church established by Christ, and its apologists often boast that there are many "Protestant" denominations but only one Catholic Church, the truth is, being the world's largest denomination, there is a lot of disagreement within Catholicism. You have pro-life Catholics, you have pro-abortion Catholics. You have Catholics who think Protestants are "separated brethren", you have Catholics who think anyone who isn't fully Catholic is eternally damned. You have Catholics who pray to Mary, you have Catholics who claim they are only asking her to pray to them. There are so many differing views within the Catholic Church that it is unrealistic to say "they are all doomed" or "they are all saved".
Of course, in reality, it is nigh impossible to say this about anyone at all. You can know about your own salvation (1 John 5:13), but because only God knows the heart, you cannot say, with any degree of certainty, that anyone else is saved or damned. You can only make a reasonable assumption based on their profession of, and consistency with, their faith.
But faith can be misplaced. In Galatians 1:8, Paul says that even if an Apostle or an angel presents a different gospel, let them be accursed. To put that as bluntly as possible, "if you preach the wrong gospel, go to Hell". And so the question to ask about Catholics isn't "do they belong to this Church or not", but rather "do they believe Paul's gospel?"
Officially, the gospel of the Catholic Church is antithetical to Paul's gospel. The message of scripture is consistent throughout: Our good works are filthy rags (Isaiah 64:6), because we all sin (Romans 3:23), and the wages of sin is death (Romans 6:23). Yet, by grace, which is antithetical to works (Romans 11:6), God gives us the free gift of eternal life, which we receive by faith, so salvation is not of works (Ephesians 2:8-9). Therefore, even the one who does not work, his faith is accounted to him for righteousness (Romans 4:5). This faith must be placed in Jesus, because while knowing no sin, He became sin for us, so that we may become the righteousness of God in Him (2 Corinthians 5:21). All who confess Him as Lord and believe in their heart God raised Him from the dead will be saved (Romans 10:9). Christ is the only mediator between man and God (1 Timothy 2:5-6), and it is He who advocates on our behalf (1 John 2:1). He is more than capable of this task, able to save us to the uttermost, because He always lives to intercede for us (Hebrews 7:25). The result of this is good works (Ephesians 2:10). Those who believe this can know we are saved (1 John 5:13).
The Catholic "gospel" is quite different. For one thing, it teaches "For "the only-begotten son of God...has won a treasure for the militant Church and has entrusted it to blessed Peter, the keybearer of heaven, and to his successors, Christ's vicars on earth, that they may distribute it to the faithful for their salvation, applying it mercifully for reasonable causes to all who are repentant and have confessed their sins, at times remitting completely and at times partially the temporal punishment due sin in a general as well as in special ways insofar as they judge it to be fitting in the eyes of the Lord. It is known that the merits of the Blessed Mother of God and of all the elect...add further to this treasure." (1).
Where does that come from? Certainly not the Bible. Yet, here we have a brand new criteria for salvation: It has to be "distributed to the faithful" by "Christ's vicars on earth". Well no wonder they historically taught that there's no salvation outside the Church. But already, we see a change in the gospel. In the Bible, it is God who distributes salvation, and He does so to all who believe.
So, the "gospel" of the Catholic Church is antithetical to the Gospel of scripture. Paul, an Apostle respected in both Christianity and Catholicism, says that those who preach a different gospel are to be accursed. What does that make Catholics? Answer: It depends entirely on how Catholic they are.
There is enough Christianity in Catholicism for Catholics to come to know Christ. It's not like Islam, which gives lip service to the scriptures only to say Christians commit shirk. Nor is it like Hinduism, completely denying the scriptures. It is a pseudo-Christian religion, meaning it is trying to be like Christianity, and as such it does give lip service to the Bible, acknowledging it as the word of God. It tries to claim authority over the word of God, but still acknowledges it. Therefore, a Catholic might very well study the scriptures. Indeed, almost every conversion story I've heard from ex-Catholics involves some degree of studying the scriptures. But here's the question: What are we to think of them prior to this?
It is my firm contention that there are Christians in the Catholic Church. In fact, a good friend of mine personally knows a Catholic priest who disagrees with his denomination, and teaches his congregation the truth about Christ. Furthermore, it is the official position of this ministry that "There are true Christians in every denomination, but there are no true Christian denominations." Yes, Catholics can be Christians.
However, due to the irreconcilable differences between "Sacred tradition" and scripture, which is the word of God, one cannot have both. As scripture says, you cannot serve two masters, and so when conflict occurs between scripture and Catholicism, Catholics are forced to choose. Do I go with the word of God, or do I go with the word of my Church? Following Catholicism inevitably leads one away from God, whereas following Christ will lead one further out of Catholicism.
References
1. APOSTOLIC CONSTITUTION OF POPE PAUL VI INDULGENTIARUM DOCTRINA, Chapter 4:7 (link).