You can read Alterman's June 2nd article here. It's about the urgent need of political journalists in the US to look for equivalence between, say, the heinous deeds of Republican politicians on the one hand and the equally heinous deeds of Democratic politicians on the other hand (or vice versa), even when no real equivalence can be found. In the latter case the demands of pretend-objectivity necessitate the creation of a false equivalence.
I wrote about that at least thrice on this blog: ten years ago, nine years ago and six years ago. From the 2007 post:*
A third pattern of interest is the "false equivalence". Suppose that I throttle my neighbor in a fit of temporary insanity, and you once forgot to send a Christmas card to your best friend from college. In the IOKIYAAR world these two deeds would be regarded as equally bad, but only if I am a Republican and you are a Democrat. (Well, your deed might actually be worse, especially if you happen to get Caitlin Flanagan to write it up.) The "false equivalence" treatment is probably the most serious one of the various patterns of IOKIYAAR, because it extends to all debate about issues so that a science debate must give equal time or space for those who don't believe in evolution or in any global warming whatsoever.
Alterman delves into the reasons for the enduring nature of false equivalencies in American political journalism. My impression is that this is a bigger problem in the US than in, say, the UK, where journalists often assume the role of a slightly hostile interrogator when interviewing politicians. That role makes providing factual corrections considerably easier for the journalist than the American "he said, she said" model which demands coverage of "both sides," even when one side clearly is preposterous.
Now how to fix that problem? It can be tricky for the reasons Alterman mentions, but it shouldn't be impossible, given that some other countries don't require their journalists to act quite so servile.
* IOKIYAAR is an acronym for "It's ok if you are a Republican". I hate hate acronyms. The acronym for that is IHHA.