Problems with modern democracy
Having given a brief overview of modern democracy, it's worth now mentioning some of the problems with them. To be clear, lots of people identify lots of different problems with democracies, and there is a lot of literature regarding it. Some people think that these problems, while significant, are solvable by making relatively minor corrections (such as campaign finance reform, or changing the voting system), while others think the whole system needs a rework.
What I want to discuss here are the problems that I identify, and I tend to think that these problems arise from the way that modern democracy has been developed - that is, we can't really solve them without changing up what democracy looks like.
The spirit of the rules tends to die
I've said that modern democracy works because of procedures and institutions. These things exist so that the way decision-making is done can be somewhat transparent, predictable and fair. Essentially these things are the rules of decision-making.
The rules are written in a particular way, and the wording is usually very careful so that it isn't ambiguous. This I'll call "the letter of the rules". But the rules are also made for a particular purpose, which I'll call "the spirit of the rules".
Because politics is driven by competition, parties and politicians want to find ways to win. While the rules of decision-making are supposed to be things that keep them working fairly, they'll look at the rules and figure out how to use them to their advantage - to find loopholes and exploits. They'll claim that they're being fair because they're working within the rules.
Eventually, the rules don't serve the purpose they were meant to serve - to keep things clear and fair. They'll need an update, but the people who used them to get power probably aren't all that interested in updating them. The spirit of the rules tends to die. What is left is a system with a lot of rules but which isn't actually fair.
I think this is likely the trajectory of most democracies - the rules get entrenched and exploited by people wanting to win, and the purpose of the rules gets left behind.
People don't need to justify beliefs
Democracy says that all people are equal. They are equal under the law, and they get an equal vote. You can use your vote however you want. This is a fundamental principle, because if people could force you to vote in a certain way or according to a certain reason, it wouldn't be your vote any more, or you wouldn't be people using equal power. So you can base your vote on your morals, on your family's morals, on who looks the best, on astrology, on a dice roll. You don't have to tell anyone how or why you voted the way you did.
But I think this has had an unintended consequence. If you can vote how you want for whatever reason you want, if your vote is of equal legitimacy regardless of the justification for it, then can't that apply to the reasoning or beliefs that underlie your vote? Can't it apply to any belief? And I think this is where many democracies are headed: people feel justified believing anything, for any reason, because that's what democracy promises. If the only way to come up with the "right" answer in a democracy is to follow a collective process, then voters are "right" in their beliefs as long as they are successful in that process. And because the justification now comes are the end, voters don't need to justify their opinions or beliefs at the beginning.
The result is that people can believe whatever they want, for whatever reason, including rejecting expert advice and empirical evidence, accepting lies, holding contradictory positions, and even confabulating claims when challenged.
In this sense, the promise of democracy has an inherent weakness. Equality of the vote was supposed to prevent domination, but instead it has reduced scrutiny and self-reflection.
Policy framing becomes more important than improvement
The function of competition in politics is so that people have different policy options to choose from. In theory, this means that parties should provide different policies to each other, and convince people that there policy is best. There are some clear ways to do this: one is to have a very good policy. There are times where policies different on fundamental values, and these will generally be different. But there are also times where policies can be compared to empirical evidence, and sometimes on these occasions the evidence really suggests that there is only one good way that the policy can be put together. In this circumstance, what are parties to do?
One option is to give up on competition and just have the same policy. The battle should then be fought elsewhere. But this might not seem competitive enough. So the other option is not to make a better policy, but try to convince people that some inferior policy is actually the better policy. They can do this by saying that the policy should be judged by a different value or a different standard of truth. So a policy that is going to deliver worse outcomes might be argued as better because it is cheaper, more practical, quicker to do. Or it could be that experts are wrong, or the problem isn't what you thought it was.
At its extreme, this means that policies tend to stand still and the framing of policies tends to change, dressed up in different language and different ways of thinking. But this also means that honesty and policy innovation start to fall by the wayside.
People fight over who are the people
When policies are competing with each other any more, there is also another option that parties can take: changing up who are "the people". If a policy is unpopular, then it's possible to still make it successful by removing groups from "the people" until the policy is popular amongst who is left. When this happens, democracy doesn't become a tussle between different policies, but about including or excluding different people from voting. There are lots of ways to do this: draw electoral boundaries in a way that disenfranchises people, making voting harder for particular groups, or make people frightened to vote. This is one of the most obvious, most egregious and last strategies in a democracy, because once the government is trying to divide who are "the people", one of the most fundamental principles of democracy is gone.
Competition for power
Perhaps most of these issues arise from the motivation to compete for power. Democracy constructs positions of power that are considered legitimate, and by creating such positions it encourages people to compete for them. The ideal is that people compete for this power in legitimate ways. But competition for power motivates that people compete in any way that the rules allow, even if it breaks the spirit of the rules. Further, it can encourage people to compete in ways where they won't get caught breaking the rules, giving at least the appearance of legitimacy. It can encourage people to reinterpret the rules and who the people are, and so on. It can also motivate completely bad faith behaviour, such as lying, coercion and fraud.
This isn't something that is unique to democracy - wherever there are positions of legitimate power, people will likely compete for it. But democracies integrate this competition into the processes of democracy - campaigns, elections and so on - and so this competition is institutionalised.
So that's my take: the institutions and procedures of democracy will tend to become fossilised and exploited, the competition will no longer be over policy but what is truth and who are "the people", and people will apply less scrutiny to these tactics because they don't have to justify their beliefs. Without periods of renewal, democracy has a natural decay.