Because it you're single, it makes sense for your tax rate to be based on your own income. But if you're married, it makes sense for your tax rate to be based on your combined income -- so it doesn't matter if you make $180K and your spouse $20K, or you both make $100K. In a marriage, you want to be able to "trade around" resources like that, instead of one partner being classified as "living in poverty" and the other considered well-off.
So if you want a tax code that seems progressively "fair", you're pretty much forced to take marriage into account.
Why?
No reason we need a marriage penalty to prevent to stop your scenario from happening.
This has real consequences when people divorce -- since it's so disincented for one partner to work while married, professional skills are likely to have atrophied. There are also social/psychological/etc. issues why more equal incomes make more sense.
What's special about their spouse giving them money, vs. being supported by any random person?
To answer your question, living off the support of "random people" is not very comfortable or lucrative. You might see people around who try to do that. We call them homeless people. They don't usually pull in enough to worry about.
We are a species that likes to pair-bond; we consider it a greater hardship to separate members of a pair than members of a looser association like friendship. The legislation reflects that. Social engineering via tax breaks are a dumb idea, but deleting the concept of marriage from law entirely is impractical and probably undesirable.
If you are a new kind of troll, I salute you.
I basically am in favor of religions being able to define "marriage" however they want (and am confident there would be a variant, if not primary variant, of every major religion which supported and another which denounced gay marriage).
The state should do something else, for everyone, with all rights handled through the state's thing.
The quick hack is to just require all new marriages also be civil unions, and not recognize future marriage otherwise. Civil union should get every current private and government benefit of marriage. Strictly religious benefits from private entities could potentially be withdrawn from civil unions (I honestly have no idea what those would be).
I have a lot more faith in a judicial solution than a legislative one. March should be interesting.
The only rights of marriage that cannot be conferred by contract are the parts that fall into the "social engineering via tax breaks" (or redistribution) category.
There's other rights, like hospital visitation, legal indemnification, etc. that also don't fall into that category.
You are correct about immigration and legal indemnification, though I question the social utility of both those benefits.
For example, my earnings go into a account I hold jointly with my wife. If marriage carried no special privileges, then we would need to keep track of how much of the income she "received" from me, to pay gift taxes. "Ok, honey, we ordered a $20 pizza, and you ate four slices, so I guess that means you received $8 worth of income..." Fortunately, we are spared this insanity, because gifts to spouses are tax exempt. This allows us to share our money like we share our lives.
Spousal green cards, spousal privilege in court, and Social Security survivors benefits are other examples of privileges that cannot be granted through private contracts, but that require the government's involvement.
Would that be a general right - any US citizen could grant permanent residency to anybody else, through a private contract?
Or would you rather eliminate the right entirely, so that if you fall in love with a foreigner, you have to hope they can make it to you through other immigration channels?
US Citizens who wish to petition USCIS to grant permanent residency to their fiancee or spouse must, as part of the petition process, sign a form that creates a legal contract with the US Government that the US Citizen sponsor must repay any means-tested social benefits the beneficiary receives. This is in addition to the filing fees incurred as part of the process.
Given that this bond must be created as part of the process, I could see your proposal as potentially being OK, except that USCIS would have to set up rules to limit this ability if the sponsor fails in their implicit duties to get the beneficiary on their feet. Basically, I see it as potentially being a privilege, not a right.
(Referring to the idea of using taxes to influence behavior in general rather than the specific; in this case, I'm having trouble coming up with any realistic (for the modern UN) way more heavy-handed approaches could be applied.)
This way, the government wouldn't have an excuse to poke its nose into every citizen's private finances.
Unless you're running a business, paying your taxes is dead simple: When you buy stuff, pay the price that comes up on the register.
Of course, it punishes people who save money, because anyone with savings at the time the law changes would be taxed twice: the (pre-change) income tax they paid earning the money, and the (post-change) consumption tax they paid spending the money.
You'd think it'd be political suicide to propose something like this (and, indeed, despite the IRS's regularly topping the list of most-loathed government agencies, the consumption-tax proposal has remained well on the fringe). But consider: The US government's inflationary fiscal and monetary policies punish savers, too, and they get away with it. Clearly, living within one's means is only for losers.
Thus, a consumption tax would hit the poor the hardest (proportionate to income), and are thus unpopular. Don't get me wrong - I personally favor them. Consumption taxes hit people in proportion to the benefit they receive from society. But they are a political non-starter for this reason.
But then you have the "they're taking away your food stamps! your social security! and new taxes" etc., even though you're giving them net more money.
One income supports 5 people in my case, but I am taxed the same way as if that income supported one person.
No system is perfect. The US system much better recognizes capacity to contribute taxation.
2) Married filing separately is not even remotely the same as filing as a single.
If two people each make $500k (nowhere close to the average/median, but it illustrates the point). They would pay the 39.6% rate on anything over $400k if single, or 2 * 100k * .396 = $79.2k. If married filing jointly, they would pay 39.6% on anything over $450k, or 550k * .396 = $217.8k. If filing separately, they would pay the same $217.8k (2 * 275k * 39.6%).
Even looking at something like each making $150k, the marginal tax rate for singles is 28% and the rate for a married couple is 33%.