Yes, some people genuinely believe and argue that the primary purpose of marriage is to have and raise children. Joe Hargrave posted a piece in September 2010 at the American Catholic website making that very argument:
Now, it wasn't that long ago that I argued against Bishop DiMarzio referring to marriage as if it were just about procreation. I also objected strongly to him seeming to treat marriage as a vocation, or job. At that time though, I didn't realize that there might be a wider group of people who see marriage in much the same way. I will undoubtedly have to return to this argument another time, but today I wanted to just get my view of marriage out there and on the record.It creates one class of people, regardless of their actions, and renders them superior to another.
I see marriage as a commitment to a relationship, a relationship built on romantic love, trust, communication, and respect. It's a way of saying to the world "we're going to stick this out and try to make this relationship work, because that's how much we mean to each other." Financial benefits, procreation, and other such things are all completely secondary to this basic foundation, and in fact not even necessary. I am well aware that this is not the historical viewpoint of marriage, but I do not think that I'm alone in seeing marriage this way. Given the vast number of book and movie romances that seem to put love first and foremost, I don't see how I could be the only person to view it this way.
When you see me arguing in support of same-sex marriage, remember that this is the foundational view, the basic premise, that I'm holding. Some of my arguments probably won't make much sense without it.