The man in Roomette 3, Car No. 11, was a sniveling little neurotic who
wrote cheap little plays into which, as a social message, he inserted
cowardly little obscenities to the effect that all businessmen were
-Ayn Rand, Atlas Shrugged
The association between Emotional Stability and conservative economic attitudes might be understood in similar, but differently-valenced terms. The positive pole of this trait is associated with emotional security and hardiness. The negative end (sometimes labeled "Neuroticism") is associated with a tendency to feel anger, guilt, and sadness. Thus, people scoring low on Emotional Stability may be more prone to feelings of guilt or pity for those in need and may, in turn, support liberal economic policies intended to help these populations.
Ayn Rand once again anticipates modern social science: Critics of the free market are more neurotic (i.e. lower in Stability) than proponents. As Gerber et al note, there is more than one way to interpret this pattern, but I'm inclined see it in cognitive terms. First pass:
People high in Stability realize that, objectively
speaking, life in First World countries is good and getting better all the
time. As long as government leaves well enough alone, our problems will take care of themselves.
People low in Stability, on the other hand, habitually blow minor problems out of proportion. Even when they live in First World countries, they manage to convince themselves that the sky is falling. Their typically neurotic response is to beg for Big Brother to save them from their largely
imaginary problems. When government solutions don't work out, they misinterpret it as further proof that life is hopeless - not that their "solutions" were ill-conceived.
P.S. If the neurotic are moderately more prone to anti-market bias, I wonder how much more inclined they are to pessimistic bias?