Partisans, or at least partisan commenters, are like hobbyists in a hundred other fields. "I collect model trains, but only Lionel from 1956-64," "Bottles. But only patent medicine," or "19th C Danish needlecraft."
"I collect factoids about Obama, but only the ones that make him look like a stealth Moslem."
"I really read up on Iraq and Afghanistan, but only the stuff that makes Bush look bad."
"I follow energy policy really closely, I've got bookshelves and bookmarks galore. But I only collect the things that say oil companies suck."
It's not just humor on my part. I actually think the mentality is similar.