They are very upfront about their biases, but they have biases nonetheless.
The "black site" narrative went completely unquestioned in the liberal press. There is zero self-policing here or signs of skepticism with liberal claims. Heck, the "clock boy" was lauded by the liberal press and Obama for being this amazing genius being attacked by racists, when it was a purposeful ruse to get teachers scared to make this kid and his dad celebrities for the purpose of helping his dad's political career and perhaps a big jury payout for "damages" soon. Only hated skeptic Richard Dawkins was remotely skeptical of these claims only to be drowned out on Twitter by liberals calling him a racist.
I think a lot of this is liberal bias. Liberals can't see their own bias objectively because they're too close to the problem, the same way conservatives can't see bias at Fox. Guardian, Independent, Salon, etc are just as bad as Brietbart if not worse, because they sell the idea of being 'fact-based' when they're propaganda outlets for a certain viewpoint which generates ad impressions and gets subscriptions via endless outrage, anti-US bias, and pandering to our emotions.
Lets stop pretending liberals don't have their army of brietbarts too.