Eugenics, if you ignore its rather ugly history, certainly does sound nice: peaceful, intelligent people harmoniously coexisting, making incredible scientific discoveries, and creating beautiful intelligent babies. I mean, most theories that plan to make the world a better place tend to sound nice. But, much like communism, the problem is not in the theory, it's always in the application. The problems in the process are so severe that you cannot just dismiss each one as "not specific to eugenics." I don't think it's appropriate to consider as a real solution until these problems can be resolved.
The Mission Statement's proposition #2 states: "Civilization depends totally upon innate intelligence." This seems to be the most important argument in the paper, in that it provides the leap between intelligence as a hereditary trait, and the degree of importance to our society that would exige such radical procedures. Hixie claims this is "scientifically proven fact." Besides the (scientifically proven) fact that nothing in science is ever a "fact" (sorry, couldn't resist), I don't think that the arguments presented are nearly convincing enough that intelligence as measured by IQ is the absolute driving force in our civilization.
Sure, IQ-type intelligence is a factor in the wonderful inventions that have propelled our society, but it is *just that*, a factor. The people who have shaped and driven our world were not necessarily always those with the highest IQs, and quite often they came from interesting and distinctly un-cushy backgrounds. Politicians, artists, writers, musicians... I don't know that the traits so important to these kinds of people can be so easily proven to be genetically inherited, and often the skills they employ are entirely unquantifiable (and at times not recognized for generations).
"Israel and Japan have higher average IQs than America, Mexico has lower, and the black African nations have the lowest. Interestingly, the very same hierarchy of nations replicates itself in America, both in IQ scores and in socio-economic status." And rich white americans score consistently higher than poor white americans. This is no proof that there's not a cultural bias - but just that you need to redefine your definition of "culture": a Japanese person's schooling and intellectual environment will be much closer to a rich american child (the kind who also scores well on these tests) than to a poor African child who only went to school until she was 10.
One of the most important skills that I learned at school was how to deal with multiple-choice tests. If this kind of test were completely trustworthy as a measure of intelligence, than why do SAT preparation courses completely ignore almost all content? Hixie states, "As far as an innate intelligence test goes, universities seem quite happy to rely on school grades to determine someone's innate intelligence." For a system like a university, of course the university is going to admit people that they believe can succeed in, and benefit from, the environment that they offer. Past grades are the closest existing measure for that purpose. But the university makes no guarantee that you do not deserve to exist if they don't admit you... you'll just have to take a rather more circuitous path to success.
Sure, us "intelligent" people would like it if everyone else in the world were happy and enlightened as well. But we need to realize that that is not the only thing that matters, and that human society as it exists now is in no position to play god on such moral scales.
Lastly, well, if we do devolve, so what? Evolution will take care of us. It always does. Perhaps the outcome might not be what we like, but that's suitable payback for our current arrogance. In purely practical terms, the most immediate outcome I see from this so-called "devolution" is an even more extreme class system. The way we rich Americans/Japanese/Northern Europeans/etc. live, we're completely dependent on the cheap labor of our "less-intelligent" cousins in South America, Africa, and Asia's less-fortunate countries: world-wide equality would completely destroy our life as it is. If the elite are really concerned with improving their life situation, they would do well to let the masses breed, and preserve the status quo. The eugenics paper shows quite clearly that the worthy always float to the top.