Why differentiate between Catholic and Christian? The only true Christians are Catholics.

St. Peter Julian Eymard – Bad Catholic vs Good Protestant
 
People often say, “It is better to be a good Protestant than a bad Catholic.” That is not true! That would mean that one could be saved without the true faith. No. A bad Catholic remains a child of the family, although a prodigal; and however great a sinner he may be, he still has a right to mercy. Through his faith, a bad Catholic is nearer to God than a Protestant, for he is a member of the household, whereas the heretic is not. And how hard it is to make him become one!
St. Peter Julian Eymard  

One can be a very sinful Christian, i.e., a "bad Christian".  This does not make one a non-Christian.  But, by the very definition of the word, a Christian is a Catholic and a Catholic is a Christian.

One cannot be a Catholic and not a Christian even though one can be a Catholic but still be very sinful and not lead a Christian life.

i totally disagree. My definition of Catholic is: one who adheres to the Catholic faith as taught by  the magesterium throughout the centuries. And if the magesterium ever becomes corrupt to the point of officially teaching heresy I am not in the Church anymore. I am almost there already. It seems most priests/bishops and e ven the pope are heretics --if not formally, than informally. They live according2 heretical beliefs, and so, they are NOT Catholic. .. whereas there are people outside the Church who love Jesus and try to live according to waht He said (not w hat they think he  said). And those people are true Christians in MY view. They still need the Church but they are far more Christian than "Catholics" who... say, believe abortion is OK sometimes --vote for Democrats... etc..