It's not that simple. The sort of advances you're talking about were indeed government impositions. But they were largely impositions from one part of the government on another part. Slavery and Jim Crow were government-enforced discrimination to begin with.
Ignoring the fact that both were overwhelmingly supported, even demanded, by the white electorate in the places they were enacted. They were not impositions by government against the will of the majority, they were government policies enacted
in response to the will of the majority. Racial bigotry was rampant throughout the US, North and South, at the time.
And contrary to your assertion, the most fundamental changes have required public opinion to change first. That change doesn't have to be total or unanimous, but politics is downstream from culture.
You're ignoring the fact that in nearly every case, only a minority of public opinion changed. The majority population either supported discriminatory legislation and practices, or were indifferent to it.
I can't find the article, but I recall reading somewhere that the tipping point for changes to public policy in representative republic is not majority support, but somewhere around 20-25% support. Only direct democracies need majority support.
No. Slavery remained because the issue was NOT one of majority vote. Northern states could not impose their will on Southern states through a direct vote.
But the issue
was one of majority support
in the states where it existed. That's why they seceded, and that is what the Lost Cause revisionism is derived from. Proponents of slavery went to great lengths to ensure that it was supported by an overwhelming majority of white citizens, regardless of the fact that few of them benefited from it, and many of the poorer citizens were hurt by its effects on the labour market. Their propaganda efforts were very effective, thanks to the prevalence of racial bigotry in the white population.
The elimination of slavery and emancipation of slaves was imposed by force on the Southern states who were adamant about retaining the institution, going so far as to mythologize it. The fact that there were many attempts to maintain de facto slavery and impose strict segregation after the war demonstrates just how popular such policies were with the majority in those states, and it took federal regulation and pressure backed by Supreme Court rulings to end them. To the point of calling out the National Guard to protect black students who enrolled in what were formerly exclusively white schools, against the violent actions of mobs of white people who opposed desegregation. (Hell, desegregation was still enough of an issue when I was a child in the '70s and '80s that there were debates over it and even some violent opposition to it in parts of the country. Eg. the "bussing" controversy.)
They would have much earlier if the North got to vote on which laws the South had to follow. Which is essentially what happened in the end.
No, it wasn't. There was no national voter referendum on the laws of the several states. Had there been so, chances are very good that slavery would have been retained since opposition to slavery was far from unanimous in the North; and some who opposed it did so on economic rather than constitutional or humanitarian grounds.
In the South, popular opposition to emancipation before the war, and desegregation after the war remained strong, and desegregation met violent opposition throughout the South for long after Reconstruction. Even in the north, de facto segregation was popular, and attempts to end it met strong opposition in many communities, albeit not as consistent or as violent as in the South.
Desegregation, like emancipation, was an example of a minority viewpoint imposed by government in violation of "democratic" principles, in service of higher principles.
We still see this today. In many of the Southern states, there is still majority popular opposition to LGBTQ rights. That's why it took a Supreme Court decision to overturn anti-homosexuality legislation in many states, and why so
a large majority states passed anti-gay-marriage constitutional amendments, and even more passed additional legislation, which in turn required a Supreme Court decision to overturn.
If you look at the graphs comparing support and opposition with regards to LGBTQ rights, most of the swing from opposition to support happened
after the SC struck down anti-gay laws. Prior to that, opposition was declining very slowly, or was remaining flat, with the majority in opposition to it.
We see that same pattern widely spread throughout a range of issues. Minority support pushes changes to legislation and establishes court tests of discriminatory legislation, and substantial changes to majority public opinion follows the changes in legislation.
When addressing Transgender rights in particular, opposition and support is fairly even, and depending on the poll, the sides are evenly matched, or there is a slight edge to those opposing trans rights. Yet legislation has been moving forward, slowly, on the federal level to support trans rights and end discrimination.
On the contrary side of that coin, the current federal government is pushing for more strict enforcement of cannabis prohibition, and more draconian immigration laws, despite both of these having minority support in the US, with over 75% nationwide supporting cannabis legalization, and over 80% supporting citizenship for DACA recipients.
Legislation is not necessarily tied to majority support of a particular policy or principle. Sometimes it follows the majority, more often it doesn't.
Sure. But the consequences of that are more complex than you suggest.
Care to explain the complexities you seem to think I am not suggesting? Anything in practical politics is going to be complex and difficult, even though the principles involved are profoundly simple.