I'm going to tread lightly here.
I believe that there are some missing important points, or at least a strong lack of clarification. Hobble and other's would be of great value here.
First of all, the word "Christian" is ambiguous. Yes, a true Christian is a Catholic- I do not deny this. In Catholic theology, the words "Catholic" and "Christian" are co-extensive; that is, they identical as the subject and predicated of a strict definition are identical, so that no man not a Christian is a Catholic and so that every man who is a Catholic is ipso facto a Christian.
However, to regard Protestants as non-Christians is wrong I believe. And this is where Clare's quotes of the Holy Fathers are useful. Why then would they have regarded them as "Christians"? Were they wrong to do so? Why?
If they are not Christians, what are they? They profess Christ, though imperfectly. So though they may not be saved, or have a harder time being saved, this does not mean they do not believe in the divinity of Christ.
I think some here are confusing what being a "Christian" is with whether or not someone is a member of the "Church" and "Mystical Body of Christ".