[toyg]

Democracy does not mean "51% rules", that's a common misconception. Democracy is about building legitimacy from as an uncontrovertial source as possible - from the clear and free choice of the body politic of a community rather than from some sort of divine revelation. Legitimacy comes from all political actors, from the minority accepting the will of the majority (because it knows its fundamental rights will be respected even in defeat, and that the "battle" could be fought again once people changed their minds) as much as from the majority itself. When we forget that, that's when the XX century nightmares rear their ugly heads.

51% on a binary choice for huge constitutional change is simply not an unequivocal result; it's well below the margin for error/fraud and reduces the legitimacy of the choice pretty dramatically. Obviously every group is free to set the rules it prefers, but taking a massive step on such a tiny majority is a recipe for strife and division. On such a small margin you can rule for a few years, not take decisions that are supposed to be set in stone and affect everyone forevermore.

Realistically, if you have more than 40-45% of the country opposed to a massive constitutional change, you are probably not getting enough legitimacy to make the process fully democratic in nature. There are further tests down the line, but a large margin is the very first one to meet if you really want to find "the will of the people" (which in itself is a troublesome construct, but that's another story). Once you get close to "2 in 3", then it's harder to argue.

[jinglebells]

Indeed. Take a look at Brexit, where only 37% of the electorate voted to leave the EU, it has been politically impossible to pass the legislation.

The electorate don't want it and the politicians can't get the votes to pass the withdrawal treaty.