Christian is a generalized label given for all believers that Christ is the son of God that came down from heaven by the power of the Holy Spirit and became man. H suffered, died and was burried and on the third day he rose from the death in fullfillment of the scriptures and is seated at the right hand of the Father until he comes to judge the living and the dead. TO BE “CATHOLIC” is to be fully Christian, i.e., a Christian that believes in the faith as Christ handed it to the Apostles and then they passed it down through their disciples by apostolic succession. They believe in the seat of Peter as established by Christ in the scriptures. So to be Catholic is to be Christian. We tend to loosely accept the marginalized use of the term Christian and allow it to be used with Protestants that reject the original faith as established by Christ through His disciples.
Many Christians actually tend to be less Christian in the sense that they seem more Gnostic in the fact that they reject the physical nature of the faith that Christ passed down. They seem to think the sacraments are nice but not real or exaggerated. In some circumstances they seem to believe that Catholic practices are not only wrong but evil. They tend to elevate the spiritual over the material nature of the faith, which is Gnostic in reality.
Those people that classify themselves as Christian but do not accept Jesus as the son of God and do not get baptized in the trinitarian form are technically not Christian by the Catholic Church’s teaching. To add another dimension to the issue, throw in the Eastern Orthodox that do not recognized the Pope as the first of many, even though the early Christians believed and taught this to be true. They do, however, see their own Patriarhate to be equal to the Pope in the same way that Catholics see the Pope. Their faith is in many ways the same as ours, tough not all of them will admit that to be true. They love to say Catholics are closer to Protestants than to Orthodox Christians, which implies that they have to correct belief as Christ passed on. My personal opinion on this is that both the west and the east make up the body of Christ in whole as the fullness of the faith. And that is where the Eastern Catholics come into play. Protestants, like Baptists, are our separated brethren in Christ.
I’m sure that comes across to some as offensive, but it is the facts in part and not applicable to all Christians that do not consider themselves to be Catholic. Some Catholics are just confused, which is sad.
I grew up with a lot of anti-Catholic sentiment, and could probably list for you every major argument against Catholicism that exists in the Protestant world. I am ashamed to confess that once bought into that. 