The "rule of one" (monarchy) was preferred by many pre-modern philosophers as a form of government. E.g. Thomas Aquinas regarded it as most perfect government, since it imitates nature (like bees have one queen).

Today, in most democracies a state of emergency can be declared, in which a government is allowed to do what is normally not.

One aspect is special powers to restrict fundamental rights of citizens, which is already justified by the existence of an unreasonable minority.

Another aspect is that the government’s power to reach decisions is expanded and streamlined by using fast-track procedures for which, in practice, the legislative body or parliament (and also the citizens themselves) are disempowered.

The government is often protected from motions of no confidence, that are either impossible or need a higher majority.

Isn't this a presumption of irrationality of larger deliberative bodies?

What justifies the assumption that abuse of power and potentially ill-considered actions, which were passed without hearing all the voices, or even against the majority of usual decision makers, are strongly preferable to potential deadlocks, slower decisions or inaction?

"The price of inaction is far greater than the cost of making a mistake." said Meister Eckhart. Sounds nice, but is it true?

So while democratic governments don't become a "rule of one" in emergencies, they considerably move in this direction. What is the justification for this?

At first, it seemed intuitively right to me, but I can't give any good reasons for it.