That is true, in principle. But there is an important difference between listening to an avowedly conservative or avowedly "liberal" commentator, on the one hand, and listening to a putatively "objective" journalist.It has been known since Socrates that fair debate can only occur between parties who are modest enough to claim only a desire or love of wisdom rather than arrogantly claiming wisdom itself. The Greek word for "brotherly love" is "philo" - as in "philadelphia," "the city of brotherly love." The Greek word for wisdom is "sophy" - hence, the word for an honest debater is "philosopher." And the word for a tendentious debater derives from the Greek for "wisdom" itself - "sophistry."
So the openly conservative (or "liberal") commentator is "philosophical," but people who claim to transcend the limited perspectives of mere mortals - people who claim the virtue either of "objectivity" or of "moderation" are sophists. Jounalism, therefore, is in principle a hotbed of tendentiousness. You will say that journalism is restricted to truthtelling and cannot be tendentious - but that begs the question not only as to whether some of what journalism tells us might actually be wrong, but as to whether the news is what is important or merely what is interesting because it is novel.
My critique of journalism is that it is arrogant in claiming objectivity, is superficial because of its deadlines, and is negative because cheap criticism and second-guessing makes its practitioners and its audience feel superior to people who make mistakes because they act rather than merely talking. And my critique of "liberals" is that they follow journalism rather than leading - and journalists give them credit rather than criticism for taking leadership positions and then scapegoating rather than leading.
Why Broadcast Journalism is
Unnecessary and Illegitimate
Media bias bump.
Here's a place to start, p79. ;^)