This kind of questions automatically enables my ranting mode! So let me rant away.

People might make stupid mistakes and vote for candidates/laws that might actually endanger their rights as free citizens. In some societies people might even go further and through the use of Democracy pave their way to totalitarianism. I think this would happen more in religion-ridden societies where you're surrounded with legions of religious nuts. In such societies lots of people like to be told to what to do rather than think for themselves and make a rational decision on what's actually good for them. Furthermore, people are raised [more like brainwashed] to follow/obey the religious scriptures. As a result they might tend to follow/obey the words of clergymen who claim they interpret those scriptures and only they know what's right and wrong.

Now let's talk about my country. I think even if the Islamic regime is overthrown, Democracy in Iran won't work. At least any time soon. I think people need to be educated first and learn critical thinking. They should know their basic human rights and never forget them. I fear in the hypothetical democratic Iran people might follow another Khomeini and make a historic u-turn again. ... sighs

I'm no expert in politics, but probably democracy works better in places with higher average education levels. My intuition is that, other than education levels, or maybe even despite them, the main factor determining whether democracy works in a given location is how well it can be set up effectively / transitioned from their current system in that location. So in other words the differences have more to do with the process of creating democracy (where anything can go wrong) and its results than differences that would apply if every location's democracy were somehow equal in construction. But I know very little about this stuff.

I don't know what's better between meritocracy and mob rule, but I think the problem with meritocracy is how to ensure that the line of meritorious people appointing further meritorious people doesn't get corrupted somewhere along the way. Probably there are ways to set up the system that mitigate corruption, but the best ways would probably only delay the inevitable until further into the future. The problem with mob rule, on the other hand, is that the common person is too ignorant to make a lot of important decisions for the state. As was pointed out in one of the comment threads, we sort of have a meritocracy through mob rule in that it's not a direct democracy but rather a democratic republic, but on the other hand, the merit of the people appointed is only as good as the intellects of the people voting. And besides being relatively dumb and uneducated in how to run a country, the people are easily manipulated by politicians who will say anything just to gain power and will do anything for money, and also by the media which (in a capitalistic country) is sensationalistic and owned by the rich who have their own skewed political interests.