There are “1,138 statutory provisions

in which marital status is a factor in determining benefits, rights, and privileges.” Turns out it was pretty easy to find a summary in Wikipedia of the “Rights and responsibilities of marriages in the United States”. 

So this is my plan:  look at this list (copied over directly from the above Wikipedia article), and think about which of these rights and benefits are appropriate for the “any two people”-type marriage and which really only make sense in the context of a mother and father raising a family (typically meaning that one of the two forgoes income permanently or temporarily due to caregiving responsibilities), and which I’m not sure of (which I think will be a large category — looking at the list, I’m not sure what all of these are about!).
 

• Employment assistance and transitional services for spouses of members being separated from military service; continued commissary privileges
• Per diem payment to spouse for federal civil service employees when relocating
• Indian Health Service care for spouses of Native Americans (in some circumstances)
• Sponsor husband/wife for immigration benefits  This is already an interesting one, since I have personal experience with this. 

• Veteran’s disability  Only makes sense in the case of a dependent spouse
• Supplemental Security Income  This doesn’t seem like it belongs in this category.  This is a means-tested benefit and (I believe) the benefit for a couple is something like 150% of a single person’s benefit.  I think Wikipedia really means disability benefits, which are larger for married couples (e.g., assuming a dependent spouse).
• Disability payments for federal employees  Really?  I hope this is wrong — if so, this is another instance of government generosity in employee benefits out of the norm of the private sector.
• Medicaid  This also looks wrong — this is another means tested welfare benefit, where two unmarried individuals are more likely to qualify.
• Property tax exemption for homes of totally disabled veterans  Does this just mean that the couple receive this benefit for jointly owned property?
• Income tax deductions, credits, rates exemption, and estimates  This is misleading.  In the case of a dependent spouse (that is, a housewife or part-time earner), taxes are generally lower filing jointly; for two earners with roughly similar salaries, there is generally a marriage penalty.
• Wages of an employee working for one’s spouse are exempt from federal unemployment tax  and, presumably, similarly ineligible for unemployment benefits, if the business fails.

• Joint filing of bankruptcy permitted  I don’t think I would call this a “right” — I would think it would be a disadvantage, that it would be pretty common that one party would have debts and the other assets, and joint filing means losing instead of protecting those assets, however minimal.
• Joint parenting rights, such as access to children’s school records  is this really a right pertaining to marriage?  Unless the step-parent has this access, it’s simply a right of parents to access their children’s records.
• Family visitation rights for the spouse and non-biological children, such as to visit a spouse in a hospital or prison  yeah, sure, fine.  I guess “non-biological children” means the step-children?
• Next-of-kin status for emergency medical decisions or filing wrongful death claims  OK
• Custodial rights to children, shared property, child support, and alimony after divorce  custodial rights and child support are based on each partner being a parent to a child from the marriage, not based on marriage itself — these same rights exist even when it’s a cohabiation arragement that falls apart.  “Shared property” — fine.  Alimony?  That’s presumably only granted these days in cases where a woman stayed home to raise the children.
• Domestic violence intervention  This doesn’t sound right — I don’t find it believable that domestic violence agencies only help women who were married to their abusers.
• Access to “family only” services, such as reduced rate memberships to clubs & organizations or residency in certain neighborhoods  OK — these aren’t government benefits/rights/programs any more.  And I’ve never heard of neighborhoods requiring you to be married to live there!  Besides, virtually every “family” rate now refers to two adults in a household. 
• Preferential hiring for spouses of veterans in government jobs  Really?  Why would this be?  Is the idea that a spouse has relocated with the soldier often enough so as cause the resume to suffer — employers being leery of the frequent job-changing
• Tax-free transfer of property between spouses (including on death) and exemption from “due-on-sale” clauses.  I guess this was what Windsor was all about — and wouldn’t have been an issue were it not for estate and gift taxes.
• Special consideration to spouses of citizens and resident aliens  This is too vague
• Threats against spouses of various federal employees is a federal crime  This is a curious one — I would think a threat against anyone due to their relationship to a federal employee would be a federal crime — or a similar threat to anyone.  (Why should federal employees be treated differently?)
• Right to continue living on land purchased from spouse by National Park Service when easement granted to spouse  This sounds more like a contractual agreement than anything else — unless “purchased” really means “seized”?
• Court notice of probate proceedings  OK, this is a “next-of-kin” issue
• Domestic violence protection orders  ???  No, you don’t need to be married to get an order of protection!
• Existing homestead lease continuation of rights  No idea what this means.
• Regulation of condominium sales to owner-occupants exemption  Likewise, don’t know.  Wikipedia is really beginning to disappoint me.
• Funeral and bereavement leave  For federal employees?  This is more of an employee benefit, then.  Or does this just mean that employers typically provide this?
• Joint adoption and foster care  Does adoption really work differently (for non-religious agencies, who don’t care about parents’ marital status) for a married vs. unmarried pair?
• Joint tax filing  This is a duplicate bullet point.
• Insurance licenses, coverage, eligibility, and benefits organization of mutual benefits society  another one that I don’t know what this means. 
• Legal status with stepchildren  And again — what is the legal status of step-parent and step-child?
• Making spousal medical decisions OK, fine, this is a next-of-kin sort of thing.
• Spousal non-resident tuition deferential waiver  why would a spouse need a non-resident tuition waiver? 
• Permission to make funeral arrangements for a deceased spouse, including burial or cremation another next-of-kin issue
• Right of survivorship of custodial trust  another next-of-kin issue
• Right to change surname upon marriage  well, really, this means “change surname without a court order” which there’s no harm in.
• Right to enter into prenuptial agreement  But can’t any two parties enter into a “prenuptial” agreement, even if it’s just an agreement prior to pooling finances or cohabitating?
• Right to inheritance of property  I assume this means “be considered the next-of-kin in the absense of a will” since anyone can inherit in the case of a will.
• Spousal privilege in court cases (the marital confidences privilege and the spousal testimonial privilege)  are there really good legal principles for this, besides just our legal heritage prescribing it?

• Social Security pension  this is based on the assumption that the spouse is dependent on the deceased
• Veteran’s pensions, indemnity compensation for service-connected deaths, medical care, and nursing home care, right to burial in veterans’ cemeteries, educational assistance, and housing  really?  I wouldn’t have thought that spouses would receive veteran’s medical care, educational assistance, etc.  That seems a bit overly generous.
• survivor benefits for federal employees again, based on an assumption of a needy widow
• Survivor benefits for spouses of longshoremen, harbor workers, railroad workers again, based on an assumption of a needy widow
• Additional benefits to spouses of coal miners who die of black lung disease  why not benefits for the estate of the deceased?
• $100,000 to spouse of any public safety officer killed in the line of duty  again, why not to the estate?
• Continuation of employer-sponsored health benefits  I assume this refers to COBRA, which is access only at 102% of full premium.
• Renewal and termination rights to spouse’s copyrights on death of spouse  don’t get me started on copyright extensions going to far. 
• Continued water rights of spouse in some circumstances  what kind of water rights expire upon death?
• Payment of wages and workers compensation benefits after worker death again, shouldn’t this go to the estate?
• Making, revoking, and objecting to post-mortem anatomical gifts  another next-of-kin issue