One of the lamest journalistic tropes is the ei quoque (Scott's idea): well, they do it too!  It's not the tu quoque, because that means "you do it too!."  This captures the gist of Politifact's defense of its sorry fact-checking:

At a Republican campaign rally a few years ago, I asked one of the attendees how he got his news.

"I listen to Rush and read NewsMax," he said. "And to make sure I'm getting a balanced view, I watch Fox."

My liberal friends get their information from distinctly different sources — Huffington Post, Daily Kos and Rachel Maddow. To make sure they get a balanced view, they click Facebook links — from their liberal friends.

This is life in our echo chamber nation. We protect ourselves from opinions we don't like and seek reinforcement from like-minded allies.

The paradox of the Internet age is that never before have we had access to more ideas and different thoughts. And yet, many of us retreat into comfy parlors where everyone agrees and the other side is always wrong. Each side can manufacture its truths and get the chorus to sing along.

Both sides do it!  Like the tu quoque, the is or ei quoque has conditions of relevance.  In this case, it is not relevant that "both sides do x" because the question concerns whether some fact f is true.  We can take it for granted, in any case, that all facts find homes in someone's advocacy.

At this point I was going to quote a section from Paul Krugman's column yesterday, but for some reason, every time I paste the passage into the piece, it deletes my entire post.  Can anyone explain this?  New York Times time bomb?  Here's the link.  The passage, despite the Times' paywall, is worth reading in this regard.  Or tl:dr: ei quoque is an empirical question.  In its usual employment, he argues, it's just not the case.  Here is a better example anyway.  Two sit-ins on the Hannity Show do the usual everyone is biased against conservatives segment.  And they come up with the following thought experiment:

BOZELL: How long do you think Sean Hannity's show would last if four times in one sentence, he made a comment about, say, the President of the United States, and said that he looked like a skinny, ghetto crackhead? Which, by the way, you might want to say that Barack Obama does. Everybody on the left would come forward and demand he be fired within five minutes for being so insulting towards a leader of the United States.

And so it goes.  Chris Matthews called Newt Gingrich a car bomber, therefore I'll call the President a skinny, ghetto crackhead.  Ei quoque; ei quoque.  There's always an ei quoque. 

 BTW, anyone a Latinist who prefers ille quoque to is quoque (mutatis mutandis)?