That's my core argument. I realize that not everyone takes the libertarian stance that I do, but that's my opinion on the matter nonetheless due to my ideals.
Now, the tax debate is a side issue. It's an attempt to understand WHY the government would want to be involved in marriage in the first place. The only point I'm trying to make there is that the IRS does give tax write-offs to married people (the only proof I need is that I pay more in taxes than my married siblings).
Even if you don't believe that and you think the amount of taxes paid is a wash at the end of the day, you can still appreciate that the government knows whether you're married, keeps track of it, and treats you differently as a result.