Then you have to pay more in taxes, having kids is more challenging, getting a mortgage becomes more expensive, immigration becomes impossible, and in some countries even travel becomes difficult.
We might be thinking of very different countries. Taxes are largely the same in most developed countries for couples or singles. Couples just have double the allowances. I'm not sure if you meant emigration, but I've lived in 3 countries while single, and I never heard this being easier married. And for sure I was never asked about my marital status for traveling.
Yes we can, we just apply independently, at the same time, as independent adults that we are, we've moved together all those times.
I've also traveled to Muslim countries, latest of which Morocco. There might be some restrictions here and there but the way you speak of marriage it makes it sound like it's the 14th century.
How? Taxes for couples are generally just doubled. You can actually save on taxes by not being married and maneuvering who claims what (house, dependants, etc).
Taxes are generally Progressive actually so the overall rate is higher for one person then two splitting.
Some major tax deductions like the mortgage deduction are per person as well, so two people with a shared income get twice the deduction as one person with an income
"Some major tax deductions like the mortgage deduction are per person as well"
This doesn't sound right.
"so the overall rate is higher for one person then two splitting."
That depends if that one person is the higher or lower earner. This statement really only works if you have two unequal salaries. Since it's progressive, you're only paying the higher taxes on the amount that is over the threshold.
I don't know what to tell you. The code is pretty straightforward. You can deduct the mortgage interest on 375 k per person. You get twice the tax deduction with two people as one.
Regarding the general taxes you are correct in that it only helps if you have two people in different tax brackets. This is extremely common