I would not date a protestant. There are several reasons.
I do believe that the man is called to be the spiritual head of the household. This doesn't mean I have to believe everything he says, but that I am called to follow his lead and to trust him with the spiritual welfare of myself and the children. To turn around and say that I disagree with him on the fundamentals of faith, which should be the basis of the marriage, and I will raise the kids my own way, is to undermine him. To me, this weakens the marriage bond at a basic level. The only way to have a marriage based on faith where I may be faithful to my husband and the Church is to only date and marry in the Catholic Church.
I was married once to someone of a different reliegion. I am not talking about I was Catholic and he was some protestant denomination. He was an ecclectic druidic neopagan (along the lines of wicca if you are familiar with that). When we married neither one of us were really practicing anything. I had fallen rather far away from the church and he didn't practice. A year later and my daughter was born. I desired to return to the Church and raise her in the Faith and he still had strong anti-Christian leanings. I could be faithful to both. I know what is is to be unequally yojed and to live in a house divided. I know my example was an extreme, but why even subject myself to the same issues?
If a man is a devout Christian, but is not Catholic, I don't necessarily agree with the argument on spiritual head. . . I could have been spiritual head as a Protestant married to a Catholic and allowed my children to be raised Catholic. . . I would consider a union with another Christian, but never outside the Christian faith. . . and by Christian, I mean active and practicing, not just a denominational reference to a Christ-based religion. . .