We know that democracy is subject to
harm by liars. Politicians willing to lie, or better still, to repeat a lie they already know some people believe (or wish were true) can create a rock-solid constituency for that lie, who will vote to support the lie they like. (see: Sarah Palin)
We know that democracy is subject to turmoil, to disunion, and to majoritarian incivility, even to tyranny by a majority given unchecked power. (see: the First French Republic, Jackson's America and Hindenburg's Germany)
We know that democracy in its purest form leads often to economic collapse, loss of trust in any form of representative government, and incessant conflict with outside powers who see the instant (and constant) whiplash of policy as either weakness or threat. (see: Periclean Athens) We know that the very loss of trust in representative government caused by pure democracy can lead to demand for autocracy by whichever politician is willing to embrace it first (or last.) (see again: Pericles' Athens, Caesar's Rome)
Basically, we know that giving We the People final political say has the potential for any of several disasters. So, what is the merit in signing onto a social contract which fundamentally demands of each of us both willingness to cede, and willingness to wield, political power?
The shortest answer I can come up with, is democracy is good for arguing.
There are essentially no political questions which have only one definitive answer. War and peace, economic and social governance all require expert opinions and frequent, expert decisions that leave mass societies well behind the power curve thanks to the cat-herding aspects of how long it takes to build a consensus versus how long it takes to build a constituency of one or three or even ten experts for a particular decision. The marvelous thing about autocracy is one man can settle a difficult question quickly.
The marvelous thing, the most marvelous and illustrious and powerful aspect of democracy, is that it takes a very, very long time to settle an argument. And in politics, that is a great benefit, one well worth putting up with how difficult it can be to herd adequate cats into the same room at the same time to get any dang thing done, because a mass society is one willing to compromise and grumble and snark and snipe and embrace incremental changes that offer the opportunity later to change its mind in one of a dozen different directions instead of settling political questions once and quickly, which is not the only alternative of course, to never settling any political question easily, quickly, or for good, but is the most efficient alternative. It is not, however, a better alternative, since autocracy has only one way to build a new constituency, and that is to remove the autocrat, usually by some form of revolution.
Republics endure. Democracy endures. Mass republics and mass democracies endure even better, and come up with more powerful solutions to more problems, with opportunities for compromise and embrace of new ideas and developing facts along the way, mainly thanks to the fact of how long it takes them to come up with any solution to any problem at all, but especially the biggest questions, like war and peace and social and economic questions that don't lend themselves well to any permanent solution. One depression or war may have a solution that merely contributes to the next war or depression; no monarchy has more than two of either in it. A democracy can go on arguing over whether we got the War of 1812 wrong and the 1893 depression right until the cats decide to come home on their own.
And that is the merit of democracy: its enduring capacity for tolerating, and embracing, differences of opinion on questions that have more than one answer. Even if that opinion is Steve King's.