hi dig,
http://ssa-custhelp.ssa.gov/app/answers/detail/a_id/175/related/1/session/L2F2LzEvdGltZS8xMzY0NDk4NTIxL3NpZC9DN2pucGptbA%3D%3D
i think there's discrimination against the unmarried all over the entitlement system and throughout the tax code. starting with the marriage deduction. continuing until after the death of a spouse (inheritance tax breaks).
it's similar to the advantages of home ownership. if you can afford a home, you get tax breaks. which means if you cannot, you pay tax disproportionately. a neat regression in the tax code.
it's not that inequalities are always bad. i think they are fine in some instances. i'm all for advantages accruing to parents because i believe that to grow children requires parents to make sacrifices. since the state has an interest in the next generation, skewing things to encourage child rearing makes sense.
i am not so sure i universally agree that the state should offer privileges to a spouse eg one who has not been as financially successful. i am not sure why that is in the state's interest.
(i am using state to mean country rather than eg Arkansas)
but there may be a justification. eg let the elderly be.