"Part" is a pretty ambiguous word.
Then again, since marriage is not required for procreation, and procreation is not required for marriage, in what sense can one argue from a legal standpoint that procreation is "part" of marriage? Both are circumstances that are often undertaken together with the same person, but there's nothing that legally binds one practice to the other.
Marriage is a 'preferred state' for procreation. 'Open to life' is a preferred state for marriage. This still is pretty much true even though we have some cultural erosion, mostly on the degree of 'openness to life.'
This is why it's necessary to use absolute terms like shifting the discussion to be around elderly or barren couples, but, again, there is no need to do so, in fact, I would say, doing so doesn't make sense either.
The point is that hatred for gays and illogical discrimination is not needed to reject the idea of gay marriage. Some people don't realize this and become ashamed as gay marriage activist present their case.
But telling people that they're personally hated when they are not is actually the thing to be ashamed of.
You know, I'm a person with five children with my wife. I have read gay community arguments detailing how you can use shaming in an attempt to overcome the opponents better angels (which is short for big family marriage reform proponents like me) who have a good strong logical position. It really is too bad. Of course, most gays, as the author points out won't do this. They respect person's with larger families and won't attempt to shame me.
I would say that more people need to be presented with the case for marriage reform in general and be asked to think if, in our culture, indeed, marriage is the preferred place for procreation and if openness to life, to some extent, at least, is the preferred state for marriage. I think most people would accept this logical position, even if they ultimately want to allow gay couples to be involved in this important support structure... which would, accepting this criteria, be more of a lowest common denominator sort of logic, which is not necessary.