It does not cost taxpayers. It costs SINGLE HETERO taxpayers who pay for all “family” benefits. If TOTAL benefits remain the same, then it comes out of the pockets of normal families and children for whom single people agreed to shoulder these subsidies. THAT is the secular objective argument againt gay “marriage” and it is irrefutable.
1) This single person doesn't remember agreeing to subsidize families of any kind. 2) Gays don't pay taxes? Did they agree at some point to subsidize only traditional arrangements? There are obviously sociological arguments in favor of subsidizing traditional families, but I'm not sure your argument holds water.