While I’m not a Catholic, it is my understanding that true Catholics aren’t advised to marry non-Catholics, if at all.
Just as the Bible says Christians should not marry non-Christians.
I am an evangelical Christian but the answer given is that a Catholic can marry a baptized Christian, like a Baptist, if permission is granted from their bishop, while marriage between a Catholic and an unbaptized person is invalid according to Rome. It can only take place in the Church if the bishop agrees to grant a dispensation from the law.
However being married to an unbeliever is one of the many grounds (psychological abnormality, stubbornness, etc.) for possible annulment (another of which is entering marriage with the intention of never having children, although that is what Mary did according to Catholicism).
Yet in Scripture, marriage is covenanted “leaving and cleaving,” and all consummated marriages are called marriage, even ones that were between Israelites and pagans, or other things which are possible grounds for annulment. Where dissolution is allowed, it is divorce, not annulment.
As regards baptism, Rome allows non-Catholics to even baptize infants, providing they use the right matter (water; except in case of absolute necessity), form (Trinitarian forumla), and intention, that of intending to do what the Church does in baptism. This is apart from (the sometimes disputed) baptism of desire.
But pressed more precisely, “intending to do what the Church does” in baptism would exclude almost all Baptists and Protestants from having been “properly baptized,” as they do not intend baptize in order to have sins forgiven, versus expresses the faith that appropriates forgiveness and justification.
Thus whether a baptist is considered to have been validly baptized can be a matter of interpretation, as can whether the baptized Protestant will be saved even if he does not convert to Catholicism, which Lumen Gentium seems to affirm, but which is difficult to reconcile with some past EENS statements.
Say if a Lutheran married a follower of Benn Hinn -- there is a difference of opinion and of belief. There can be conflict, but doesn't have to be if both partners go into the marriage knowing the differences and accepting it
A cousin of mine married a Hindu and they've been married for 15 years, happily.
Even among Christians -- if a CAtholic marries an Orthodox or a Lutheran, the differences as not as acute as say for a Lutheran to marry a Baptist
I've never heard of any one being advised, once they have decided to marry, against marrying a non-Catholic
All that they are taught during this pre-marital course is "recognize the differences and accept it, or don't get married" -- and it's not only religious differences, but also other topics -- children, money, living with the family etc. -- people should go into marriage KNOWING about the other person and accepting it -- if a Catholic/Lutheran marries say a Baptist, then the Baptist should recognize that the Catholic will go for mass and that the Lutheran believes in the True Presence of Christ in the Eucharist
They don't have to believe it, but accept that their partner does. Otherwise, it is not going to be a successful marriage.