Taibbi does not like Trump, not even in the sense of the enemy of one's enemy being one's friend. But he's a "whistleblower" of a sort himself.
Taibbi has essentially put forth the challenge for liberals to decide to what degree the ends justify the means. This is no small matter; what people say they're OK with now will have an impact on what will be OK governace if their party takes control of the Congress, or gains the White House. Democratic apologia for ends-justifying-means measures to drive Trump from office will give license to the GOP to carry out the same sort of Witch Hunts against Adam Schiff, James Comey, and a long list of Deep Staters. That these people are all scumbags, every last one of them, does not justify that our Congress drop everything to investigate them. That the GOP started this with their e-mail and Benghazi snoopapaloozas against Hillary Clinton doesn't make what Democrats have done, and plan to do, OK.
The reaction to Taibbi by much of the left here reminds me of the Right's condemning The Dixie Chicks when they openly criticized George W. Bush at a performance during the Iraq War. The hue and cry over this wasn't because of what Natalie Maines SAID; it was because who The Dixie Chicks WERE and what was expected of them. They were Coumtry Music, they were on "Team W". Didn't they know that? The right could care less what Green Day might say, but this was a defection from the team. That's how Taibbi's criticism is viewed; it's heresy from a team member. That, of course, begs the question of what "team" a working journalist is suppost to be on.