Additionally, why is a meritocracy even desirable? You don't choose your parents, you don't choose your genetics, you don't choose to be born able-bodied or not, so why should you be rewarded for those things over somebody else? Under a meritocracy, a kid born with a 60 IQ and who's physically disabled would have a pretty bad life compared to an able-bodied person born with an IQ of 150. Since neither choose their lot in life, why reward one over the other?
The only kind of meritocracy that makes sense to me, is to measure how hard a person works, with the understanding that some people will have to work harder to accomplish as much as others. But again, I don't think that's possible to achieve, and likely never will be.