Quantcast gathers data two ways, one is direct record collection (doesn’t look like it does that with FR per their disclaimers), second is analytics of traffic based on sites that do collect data. Basically, for example, they do collect this data off TownHall, they see traffic from FR to TownHall so they compare that traffic and use it to compile a demographic profile for FR. (a lot more complex than that as it compiles data from tens of thousands of sites).
Basically, you don’t have to give a lick of data for computers to get an idea of the site’s demographic make-up.
According to their data that diverse group over at DU are full of it.
Free Republic
African American
There are more African American visitors here than average
DU
Caucasian
There are more Caucasian visitors here than average