merely earning a Bachelor's degree is a golden ticket. People with average and below average IQs are getting just as much of a financial return out of their 4-year degree as those above the 85th percentile. This suggests many more people of marginal ability should be seeking a Bachelor's degree, not less...people with 4-year degrees earn much more than people with 2-year degrees and trade jobs at every level of IQ.
He did his own research, using data from the General Social Survey. The results support Golding and Katz (we need more college education) and contradict Murray and Kling (we need less). One point I would make, that Malloy sort of alludes to, is that when someone of average IQ completes college, this could be due to (a) measurement error of the IQ indicator (they really have a higher IQ) or (b) unusual persistence or other characteristics.
It could still be the case that, at the margin sending more kids to college will not result in more kids graduating college. The additional kids you send may have neither the intelligence nor the other characteristics needed to graduate.
Still, a very interesting piece of work. Plenty of journal articles have been based on less.