Why does Think Progress disable/inhibit opposing viewpoints ability to post on their site?

I decided to enter the comment/discussion on a Think Progress posting, only to have my posting priveleges messed with (see comment section of Olbermann gives 10k to ManCow article). If I got to the site without logging in, it works perfectly, but depending on the computer, now if I log in I either can't see the comment section, or it won't let me type in the comment box. Is this what happens when someone offers an opposing viewpoint on their "progressive" website? Is reasoned disagreement so deleterious to their claims that they must silence it?