I thought several people have been willing to talk about it? I've tried to explain my concerns with legalizing same-sex marriage, and to generally do so from logical and legal point of view, rather than just citing morals/theology/etc. Apparently I haven't done a very good job of it!
In a nutshell (and this is probably going to be lame, because the argument is really complicated, and I have a tendency to get long-winded), I think that we need to either define marriage as between one man and one woman, or if we're going to redefine it and say same-sex couples can marry, then marriage needs to be opened up to everyone. Polygamous couples, cousins, brothers and sisters, etc. I just don't think you can have it any other way. People are arguing that people should be able to marry the person they love. Okay, then why can't close relatives get married? Why should society put restrictions on THEM- isn't it discrimination? They're only two people, not a polygamous relationship, so there shouldn't be all of the legal issues posters have cited regarding multiple spouses, inheritance laws, etc. It is legal in France, Portugal, Sweden, and I don't know where else.
It seems to me that either marriage should be open to everybody, so people can marry whomever they like, or we define marriage as it has historically been defined- between one man and one woman for the joint purposes of mutual fulfillment (ie love) and of raising children together. This is essentially what I was trying to argue upthread, and I think gatorsmom and a few other posters (can't remember who- maybe even you, Wellyes?) were also trying to point out.
However, I also think that in this day and age, it is really hard to argue for this traditional position, largely due to the fact that children no longer need be a natural result of marriage and sexual relationships. Birth control enables couples to avoid having children, and couples with fertility difficulties are able to take advantage of reproductive technologies enabling them to have children. Please understand that I don't think that all of things are inherently bad- I'm very thankful that people, several whom I know and love, are able to have children because of advances in reproductive technology.
HOWEVER, one consequence of this is that in many ways, having children has essentially become optional and/or self-determined for married couples. Couples can decide not to have children, or couples can become parents without going the "traditional" route. Because simple biology isn't as much of a factor anymore for when/if a couple has children, the bond between the unitive and reproductive aspects of sex is eliminated. Sexual pleasure itself becomes the main purpose and goal of sex, and the other natural, biological purpose- having children- is irrelevant. Thus marriage, which has historically been a vehicle for the begetting and raising of children, for the good of society, has come to be seen as a union based on affection and mutual fulfillment. Don't get me wrong, I'm glad that we live in a time and place where people generally do love the person they are marrying. But when you take children out of the equation and make them optional, then I do believe it is much more challenging to argue for traditional marriage.
That probably didn't make any sense. Like I said, I tend to be long-winded. But all that to say, I think that you either need to take the traditional view of marriage (which as I tried to explain at the end, is challenging to argue for when you take children out of the equation and make marriage based solely on feelings and personal fulfillment), or you need to open up marriage to anyone and everyone. I see it as all or nothing.
ETA: I'm done with this discussion. I've been glad to be a part of it, but at this point I'm just feeling drained and nitpicked, and I've got other things I need to do today.