Nope, I don’t think that marriages that produce children are any more special. I also don’t think that whether or not a couple procreates is something that the government should concern themselves with.
I think the argument here proceeds from the question of the benefit to society of having the next generation of citizens (1) procreated, (2) cared for and protected, and (3) raised in environments other than ‘wards of the state’.
This approach raises a number of questions: is this explicitly (one of) the motivation(s) of the state in regulating marriage? if it’s not an explicit motivation, can it be inferred in the various statutes and juridical decisions that have been made manifest?
The ‘historical’ question comes into play here: if it can be asserted that these considerations were once part of the rationale for the government’s participation in the institution of marriage, have these considerations declined in importance to the point where, today, they are relatively irrelevant?
These are interesting questions. However, another question is necessary: even if government
had been motivated by these concerns, are there additional, more fundamental reasons present to justify the state’s role in marriage, that perdure even if the social considerations of ‘procreation’ (and ‘protection of women’) have faded?