It is a useful theoretical concept that has absolutely no grounding in the reality of human incentive structures, randomness and extreme path dependence. Meritocracy can only exist if all humans are equal - as in perfect clones of each other - prepared in the exact same way, at the exact same time.
Given the proposition that 'a persons life prospects should not be decided by factors outside of their control or for which a person cannot claim personal credit' (i.e social status, inherited wealth, race and other accidents of birth) a meritocracy proposes a system where people are rewarded based on their efforts, and if everyone can start on equal footing with the same opportunity to advance, then the results are just. However, some studies have shown that even our motivation, work ethic and conscientious drive is in fact outside of our control and can be affected by such arbitrary factors such as birth order. Children who are first in birth order are more likely to be hard working. Therefore, a system which rewards effort in this way is not just, because effort and hard work is not something we can claim credit for.
-- http://en.wikipedia.org/wiki/Meritocracy
Check and mate.
People continually say they are for equality of opportunity and not for outcome (bullshit!). That is impossible.
Hence we modify the outcomes (welfare/taxes/public goods/roads/sewers/national defence etc.) to mitigate the messier parts of humanity and stabilize societies from uprisings and violence. If the people don't eat bread - the people get angry - and heads roll. Just ask the French!
Meritocracy began its life in an essay parodying the self-same concept that brought its name into existence.
Although the concept has existed for centuries, the term meritocracy was first coined by British politician and sociologist, Michael Young in his 1958 satirical essay, "The Rise of the Meritocracy"
-- http://en.wikipedia.org/wiki/Meritocracy
It is such a ridiculous concept I have no idea why humans believe it. Actually I do - it's called the Just-world hypothesis (http://en.wikipedia.org/wiki/Just-world_hypothesis) - a systematic and problematic cognitive bias seen throughout human culture - Karma/Santa Claus/Heaven-Hell/Justice systems and many others I am sure. It is a derivative of the fundamental attribution error (http://en.wikipedia.org/wiki/Fundamental_attribution_error).
Meritocracy is bullshit. Always has been - always will be.
Along with a ton of other systems/ideas/thoughts that I won't go into to avoid unnecessary down votes and the brutal thought pain I might cause others :D.
In the words of sociologist Laurie Taylor:
“The hideous thing about meritocracy is it tells you that if you’ve given life your all and haven’t got to the top you’re thick or stupid. Previously, at least, you could always just blame the class system.”