David Flanagan has written an article on Blogcritics called Blogcritics.org: Accelerating The 'Roe Effect'
While I don't at all agree with his arguments, I found it a very interesting read on the ideas surrounding changes to marriage.
My main argument I guess is against muddying the religious concept of marriage with the secular benefits bestowed by governments.
Personally I believe it is discriminatory to allow some people to obtain benefits when living together in a comitted relationship while others don't. I also question the rationale for restricting this in any form to two people. The main issue here is whether the government at all should sanction specific forms of relationships over others in this way, and my answer to that is no.
When it comes to the religious idea of marriage, I couldn't care less. If a church refuses to marry two (or more) people, then that is their business.
If someone chose to rename "civil marriage" to "government approved relationship contracts" or whatever, then fine. What it's about is rights and responsibilities in what is essentially a contractual agreement.
The very idea that marriage is a union between one man and one woman is a religious idea that there is no justification for keeping as secular law
Separation of church and state is a protection for those of us with different world views - whether atheists (like me), muslim, or any other that are not tied to the Judeo-Christian image of marriage.
If anything, disconnecting the two might make more people open entering agreements covering their relationships, contrary to the current situation where marriage is an institution that is gradually becoming less important.
The idea that Christianity spread by having more children does not benefit Christianity now. On the contrary, muslim families are much more likely to have many children, and tend to be much stricter than Christians with regards to abortion.
Muslims are also much more likely to support polygamy than Christians, given that the idea of up to four wives is well ingrained in many parts.
At the same time I doubt this has much effect long term, otherwise how does one explain the significant decline in fundamentalist Christianity in terms of percentage of the population?
Conservative and fundamentalist Christianity is losing out because people are increasingly more critical to their parents viewpoints - rebellion is an accepted part of youth culture, and access to more varied viewpoints have made people more and more likely to make up their own mind rather than blindly accepting what their parents told them.
We're at a stage today where most "christian" countries face a situation where regular church goers are now in a minority and people largely pick and choose to make their own version of Christianity that is significantly watered down over just a few decades ago (ask people how many believe in hell for instance)
This is a trend that's been ongoing for hundreds of years, and is unlikely to be stopped by some slight changes in the number of children born to various types of parents.