There are a variety of ways that democratic governments are structure that make this an inaccurate characterization of how things work.
The US, for example, apportions representatives and votes for President in a way that overweights less populated states, and there are various aspects of parliamentary systems that help avoid landing in a two-party system where a simple majority gets the say in everything—they force compromise and coalition building among disparate groups. Additionally, Constitutional systems will enumerate the rights of its citizens such that they cannot simply be taken away by a simple majority of any body.
Democratic countries are also basically never "pure" democracies where everyone votes on every decision as in your Plato's ship analogy—we elect people who audition for the role of running the ship, ostensibly those among the people who are best suited to the task.
> , Constitutional systems will enumerate the rights of its citizens such that they cannot simply be taken away by a simple majority of any body.
Only if those are enforced. The wealthiest are the ones with the power, as they can pay for the guns.
Again, we're talking about a functioning democracy.
If you take an example of a non-functioning democracy, it's not a good way to describe a functioning democracy.
So how do you stop a function democracy becoming a non functioning democracy
Ultimately it comes down to who has the power. The more that power is concentrated the more fragile it becomes. It doesn't change overnight.
> So how do you stop a function democracy becoming a non functioning democracy
I wish I knew :-). A functioning democracy seems to be an unstable equilibrium.
But it remains that a functioning democracy is what we should aim for.
> Ultimately it comes down to who has the power.
Well it starts with the people giving them power. Trump did not seize the power in the US, for instance. He was elected. Twice.