He contrasts our common idea of consensual, e.g., I order something from Amazon and Amazon sends it to me, with the government. One example he uses is that I may vote against a particular law, or a politician who promises to impose that law, and yet if more people vote the other way, the law will be imposed upon me against my will, the exact opposite of what we mean by "consent" in other matters.
He points out that we have no reasonable way to opt out of government control. Moving to another country simply doesn't solve the problem.
Additionally, he points out, the government has no enforceable duty to us. The USSC has repeatedly ruled that the police have no duty to protect you; if they ignore your 911 call and you die because of that, too bad.
So, in short, this is rather like Amazon simply deciding to charge you for things, never sending them, and you having no recourse. If it were not government, backed by overwhelming force, we would never stand for it.
He covers a number of other reasons why current democratic governments are non-consensual and then moves on to why that is important.
... the nonconsensual nature of most government power does not prove that government is necessarily illegitimate, or that democracy has no benefits. Government power might often be justified on consequential grounds, such as its ability to increase social welfare, provide public goods, or curb injustice. ... And democracy still has a variety of advantages over dictatorship or oligarchy. Among other things, those types of regimes are usually even less consensual than democracy is.
But the lack of consent does undercut arguments that we have a duty to obey the government because we have somehow agreed to it or because it represents the “will of the people.” When the government makes unjust laws, it cannot so readily claim we have an automatic duty to obey them, regardless of their content.
Moreover, if government power must be legitimized by its consequences rather than by its supposedly consensual origins, that strengthens the case for imposing tight limits on the state in areas where the consequences are negative, or even ambiguous. ...
And this is pretty much where he leaves it. I wish he would have explored what a consensual government would look like, or even if such a thing is possible. One of his sources, Georgetown Professsor Jason Brennan, argues that it is not.
Brennan, according to his bio, is currently writing two books with the titles Against Democracy and Global Justice as Global Freedom. I can guess where he goes already.
So what about consent and the justification for democracy? What about those consequential justifications? What about the idea of the "social compact / contract" for those who were born into the system and had no say in writing that compact or contract?
Somin is a libertarian, and I also think that's where this leads us: All government is violence: vote for less.
But. I also question the idea of consent as applied only to particulars. Instead of this particular law or that particular tax, consent could be to the system. In this case, democracy looks more like a team sport. I don't consent to the other team scoring a goal -- in fact I do my best to make sure they don't. But I do consent to play the game and abide by the rules and the referees' calls.
That is weak, though. In a sport, if I decide I no longer want to play or abide by the rules, I can quit and do something else with my time. Not so with government. This is a sport we are forced to play. Again, I think the coercive nature of the relationship argues for the minimum government necessary. The less the government impacts my life, the more I can live it in consensual relationships outside of government control. It isn't perfect, but it seems a lot better than the alternatives.