I believe that the equating of Protestantism and Christianity in the minds of many people has been one of the greatest victories of Satan in recent times. It is a major contributing factor to the spread of the sin of religious indifferentism and liberalism. It also helps prevent Protestants from recognizing their errors because they mistakenly think that they are just like the Christians which are called Christians in Holy Scripture. And if it is indeed true that Protestants rarely called themselves Protestants, then they are constantly deceiving themselves (which plays into Satan's hands).

The corollary of this truth is that Catholics may NOT be called Catholic Christians. Roman Catholics are Christians and Christians are Roman Catholics. To use the term Catholic Christian is a redundancy and the adjective Catholic makes it seem as though there is some other type of Christian (or that there is in fact more than one type of Christian). Although thankfully, to my knowledge, not in widespread use, it is not unknown for Protestantism to be called Protestant Christianity.

This corollary is very important because while it may be less damning than calling Protestants Christians (at least a material heresy), I believe that it is much more subtle. No less an important and orthodox a personage as Fr. Michael Muller has used this phrase (in his famous work The Catholic Dogma: Extra Ecclesiam Nullus Omnino Salvatur).

While it is true that Catholics are Christians, in these times I believe that the best policy is to identify yourself as a true Roman Catholic because most people who do call themselves Christians are Protestant and it is not good to support Protestantism by affirming whomever you are talking to in their errors by given them an illusion that you support their errors because you seem to believe them as well. Unfortunately, even calling yourself a true Roman Catholic nowadays can be ambiguous (as many sedevacantists, etc. do), but hopefully a typical follow-up question, "So where do you go to church?" will give you the opportunity to proclaim your beliefs and perhaps spread the gospel.

To conclude, it is vitally important that you never call or even think of Protestants as Christians. If somehow through the force of habit you slip up, correct yourself in your mind because this is the path to religious indifferentism and may indicate the taint of liberalism.