Capitalism is a meritocracy; those people who are best-suited to the capitalist system rise to the top and are given unchallenged executive authority. If you are talented, you succeed and receive the power to make dictatorial decisions. You can choose the direction of the system, without recourse to those for whom you are responsible. You can punish and reward based on merit. And talents, or lack of talents, are rewarded and punished proportionately. Those people who don't perform effectively are excluded from power and benefits. Capitalism assumes that we are not equal and rejects the majority of the community as unskilled, ill-equipped and unsafe and reserves the benefits and responsibilities for the talented minority.
Whereas democracy is an all-inclusive process where everyone has equal power to select the progress of the system. Everybody is trusted with the power to choose the best direction. As democracy and modern technology develop we are extending more and more executive power to the whole of society. Those people who previously had no voice are finding their voice. And we can see many new grass roots movements that the 'talented elite' find disconcerting, ill-informed and dangerous (Tea Party, Palin, Anti-global-warming, Fundamentalism etc etc)
Is post-modern democracy in danger of giving too much executive power to the people who, under capitalism, are marginalised on the grounds of gross inadequacy?
I would agree that it is difficult to make a straight comparison between capitalism and democracy. As stated above one is a political system and one is more of an economic system. In answer to your last question I would say we are more in danger of too much greed than inadequacies.
In theory, your comparison makes sense, I just disagree with your premises that capitalism is a perfect system of natural selection, or that democracy is a perfected form of popular measurement and participation. So my short answer would be, I guess, that if we ever get real capitalism or true democracy, then we'd know.
My answer in the abstract is democracy, which is not (as much anyway) motivated by greed and profit. It is quite different to reconcile those two things with honest and true allocation of power.
Also...this question is comparing a political system with an economic system. The assumption seems to be that capitalism and democracy are mutually exclusive...which they aren't necessarily. Our own country represents an attempt to marry the two ideals. Whether or not we achieve that is another story altogether, but I don't see how the two are incompatible in theory.
Your final thoughts lead me to believe that your question is more about technology/media access. As we have more information at our fingertips, we have more opportunities to affect political change. Yet I don't think more accessibility implies that people will be more or less informed. For example, we now have several 24 hour news channels, but if you only watch one, you may only get part of the story & will thus be uninformed. Or, you may continually seek the latest information, and use that to be an informed and active political participant.
Finally, all of the "grassroots" movements you named are decidedly from one end of the spectrum. Some (the Tea Party, for instance) are bankrolled by large companies, & therefore cannot really be considered grassroots at all. There are some very real, very well informed groups of grassroots organizers- run a search for the NetRoots convention taking place right now in Las Vegas. Indeed some of these ideas/ movements you mention (for example, religious fundamentalism in any form) are disconcerting not just to the "talented elite" (whomever they may be), but to all informed citizens.
To sum up: Capitalism and democracy are not mutually exclusive, and it's difficult to compare a political system to an economic one, although they may be intertwined.
The idea that people who do not come to power under capitalism (the ones who do not become the CEOs) are grossly inadequate is not really an accurate one, in my opinion. In capitalism, firms look for people who have specific skills. The people with these skills are better for these firms, but they are not necessarily better citizens for a democracy.
Think of an NBA team. They are a meritocracy and the best players become rich and famous. But that does not mean that these players would be more competent as citizens of a democracy than the better basketball players.
It may be that people are too poorly informed to be good citizens, but it is not related to the reasons why they don't advance in their firms.