I think it is less about the religion itself and more about the beliefs the two people hold.
My husband is ELCA. I’m Catholic. We’re both devout in our beliefs, but he and I agree on important things like birth control (or lack thereof), the importance of raising our kids Catholic, etc etc. He’s a fairly traditional person whose issues with the Catholic Church are pretty limited.
I’d rather be married to a devout Protestant than a lukewarm Catholic. I’ve dated lukewarm Catholics, and we bumped heads over more issues than my husband and I ever have. How would you explain those types of differences to children? My husband is the only person I ever dated who didn’t believe in using any birth control other than NFP (just as an example).
Before marriage, you need to ask yourself: “Is this person going to make my growth in faith harder or easier? What effect am I going to have on his(her) spiritual life? Just in general, will we help each other grow or not?” As the pastor of our current parish puts it, marriage isn’t just about raising a family. It is about getting each other into heaven.
The second question to ask is this: “Is this person going to make parenting harder or easier?” Include passing your faith on to your children in that equation.
I married a baptised non-Catholic. He had been given essentially no religious upbringing, but he valued religion and wanted our kids to be raised in mine, since he had none to give them. Nevertheless, he had been instilled with many virtues, like compassion, generosity, honesty, honor for his parents, loyalty towards his family, reverence, and many other qualities, qualities that men with the benefit of a Catholic education aren’t likely to pick up later, if they haven’t taken hold by young adulthood.
My husband has always been a gem. I could not ask more of him in terms of helping me and our sons in growth of our faith. Still, it is not easy being the only religious “expert” in the home. It is not easy having most of that leadership role. All I can say is that if he were a Catholic and lukewarm, it would be a *lot *worse. I went to a Catholic High School, and there were some wonderful guys that would have made splendid, devout Catholic husbands. Unfortunately, the only one that wasn’t a relative or wasn’t intimidated because my grades were better than his was a neighbor in my class who seemed too much like my brother to date. The others, quite frankly, would probably have made my spiritual life and duties as a Christian mother harder, not easier. At that point in their lives, their faith was not a very high priority for them. When choosing spouses, a change for the better over the course of life, while it can happen, is not the way to bet.
A friend of mine is fond of the old saying: “Don’t marry for wealth. Hang around rich people, and marry for love.” Would that we took that advice when it comes to the riches of faith. Perhaps if I had attended a Catholic university, I’d have run into more Catholics who didn’t share my family tree, but that is another story, and too long to go into here.