Elsewhere you'll see they honestly and clearly state their intention to promote left-wing liberalism. They aren't pretending to be objective, balanced, or factual.
Holding a set of beliefs doesn't disqualify you from being objective, balanced or factual.
Everyone has beliefs - some subscribe to a classifiable set of beliefs. This journal is a collection of people who share some beliefs around liberalism - and they declare it.
Of course this means that they'll tend to see things through the prism of their beliefs - but everyone does this. At least in this case, they're honest and upfront about their beliefs, so you can take those into account.
They're going to pick stories of interest to liberals, and they're going to give liberal insights into events - but that doesn't mean they can't be reasonably objective, balanced of factual.
I say 'reasonably' because nobody can be completely objective, balanced or factual. Everyone is influenced by their preconceptions, experience, and by their imperfect knowledge.