You do realize that the people can consent, either through action or acquiescence to forms of government that are not democratic don't you?
I again point you to the examples of Nazi Germany, Fascist Italy, etc.
This is worth some serious meditation. If the Fascists and Nazis through force or lies induced the Italian and German electorates to do something they did not wish to do, or were unaware they were doing, then there is no theoretical problem. These acts of deception or violence render the parties that perpetrated them illegitimate as governing bodies. So I don't suppose you mean that: I imagine you mean that the Italians and the Germans knew what they were doing, and a plurality or majority of them did it freely and intentionally.
They gave up the power of voters to elect their countries' leaders, and intentionally placed these countries in the hands of individual dictators. So, if the people are sovereign, and the people did that, then doing that must be legitimate, because the acts of sovereigns are by definition legitimate. I suppose that's what you mean.
This principle is in fact raised in one of the very earliest texts that enter this discussion - the "Declaration of Arbroath", 1320.
The composers of that document proclaim their allegiance to their "Prince, King and Lord"; and they will "adhere to him in all things". But what if he seeks to transfer his sovereignty to the King of England? He is, after all, the legitimate sovereign of Scotland, so can he not do what he pleases with this sovereignty, because it is his possession?
No, says the Declaration: if he manifests any willingness to do that, the signatories of the Declaration will "at once strive to expel him", as their enemy, and as
sui nostrique iuris subversorem a
subverter of his own rights, and of ours.
Majorities of voters in countries with parliamentary governments are perfectly capable of disgraceful acts, just as individuals are capable of disgraceful acts. We have seen examples of this recently. Some such acts are legitimate and some are not. I can give my money away to an unworthy cause, as long as I know what I'm doing, and the money was not extorted by force or deceit. But I can't sell myself as a slave. I have personal freedom, but I'm not permitted to relinquish it. It is not my possession in the sense that my bank account is my possession. No court would ratify such a contract.
Therefore, although the Germans had a right to elect the Nazis, in any given election, they had no right to transfer to an individual their own right, and the rights of future generations, to choose the government of their country.
Also it is very noticeable that as soon as Hitler had secured power through an election, he abolished elections. The operation therefore looks like a swindle sustained by deceit, which makes it
ipso facto illegitimate; but even if the German voters were acting with full knowledge and intent in voting for him, what they did was a violation of their own sovereign power. The German voters were "subverters of their own rights" in that case ... and subverters of the rights of their children.