Political moderates are less intelligent?

I made a comment to the effect that political moderation tends to correlate with lower intelligence when looking over survey data on attitudes toward unpopular speech. This assertion didn't come out of a vacuum, when mining the GSS there were repeated indications that moderates were somewhat stupider than they should be. But here's the WORDSUM scores for whites separated into moderate vs. non-moderate classes (liberals & conservatives aggregated in the second).