My personal opinion on this topic is as follows :
I could not imagine being soul mates with someone if we could not agree on that one thing which is most important to the soul. How could I love someone so intimately if I could not love their faith, which is single most important thing to a person's heart. How could she love me if she could not share my love for Our Lord in the Blessed Sacrament and for His mother? Faith IS a major part of who we are. When we marry (and dating is preparation for marriage), we must love 100% of the person we marry. I don't think it would be wise to divide one's heart in such a way.
Likewise, having two parents of different faith has a greater potential to create cognitive dissonance in children. Sure, we promise to raise our children Catholic, but are we honestly going to say Mommy or Daddy is wrong and that it is not acceptable to profess their religion? So you either put down a major part of who one parent is, or you give the impression that it really doesn't matter what religion you profess. Both have the potential to be dangerous to the faith of children.
And sure, things can happen during a marriage--people change--and you must deal with it with love and sacrifice and patience. But it's not right to seek the path to martyrdom--if it happens, you embrace it, but most often you seek the path that will fulfill your vocation best. The principal ends of the vocation to marriage is to produce new members of the Body of Christ and citizens of the Heavenly Kingdom, and to sanctify both spouses through total Christian love in this Holy Sacrament (I know that sounded mechanical, but I don't have the space to go into the detail necessary to draw out the true beauty involved, so that will have to suffice). I just think the best way to fulfill these ends is through marriage with someone else who believes it is a holy Sacrament and who agrees on the one and only narrow path that must be taken to be saved.
On the flip-side, the sacrament of marriage is not to be used as a tool to evangelize the other person. You have to ready to accept a person as they are--going into a marriage hoping to change someone is a recipe for disaster and misery.
I'm not saying a marriage between a Catholic and non-Catholic can't be done successfully, but I think the risk of problems and strife is magnified greatly by a conflict of faith (especially if both people care greatly about their faith).
I think one reason why the Church changed her discipline and allowed Catholics to marry non-Catholics is because in this age where indifferentism is rampant, Catholics were more likely to sacrifice their faith, than their relationship with a man or woman. At least now, there's a chance that by remaining united to the Body of Christ, the spiritual benefits flowing through It will bring the one to salvation and the other to the saving truth as well.