Pro Arguments from the Left

What follows are the arguments for gay marriage that come mostly from the left. I openly admit that my readings from the left aren’t as extensive as from the right. I’ve goggled around and found very little. My education has come from talking to people around me, reading the letters to the editor in the Strib and (most importantly) from gay friends of mine that want to marry. As always, comments are welcome.

L1. Marriage is a civil right – This is the big argument from the left. So big that it almost excludes the need for other arguments. The argument is straightforward. Marriage is a civil right. If gay couples want to marry, they should have the right to. Excluding them is a violation of their civil rights. Simple, no?
The problem I have with this is that I’m not sure I agree with the premise. I’m not sure that marriage is a civil right in the same way that free speech or the right to bear arms is. If marriage can be allowed or disallowed based on the age of the couple are their rights being refused? It doesn’t seem that way to me. Also note, the above argument practically begs for polygamists to demand similar rights. Even adding a numerical limit seems slight. If gender isn’t important enough to treat differently, how can the number of people involved?
L2. Add-ons – By this I mean a number of things that are automatically granted to married couples by denied gay couples. This category is for things like tax breaks, inheritance, visitation rights and so on. I find this to a pretty strong argument but not necessarily leading to full out marriage. A well crafted civil union law could take care of this.
I should also note that I find this to be a peripheral argument. The gay couples that I know want more than this. Their desire to marry has more to do with their love for each other than a desire for tax breaks.
L3. Validation – This is the mirror to the argument against state recognition. Gay couples want validation that their relationship is approved. Again, this is the one that makes ‘marriage’ the battleground rather than civil unions. Frankly, I’ve had a hard time getting my head around this one for pro or con.
L4. Loving Couples Marry – Marriage is what couples that love each other deeply do. Marriage involves stability, emotional support and a general blending of lives together. Gay couples have enjoyed de facto marriage for decades. What they’ve had is the same thing straight couples have enjoyed (minus the add-ons). I find this argument persuasive too. There were a number of reasons that made me want to marry the FP Gal. Most of them were abstract and would fit into this argument. The same thing applies to the gay couples I know who want to marry. (This isn’t as left/right as the other arguments but it so obviously belongs with the pro-arguments that I put it here.)