I would slightly challenge some of this premise. Aside from the poor saps all over the country that have no cable access for alternative news, these viewers of the bigger networks, are essentially cheerleaders. There is no way I would believe that half of the viewers of ABC, NBC, CBS, & CNN are not ideologically vested. After the years of out and out lies from all of them, you simply cannot be a free minded critical thinker if you watch any of them for any other reason than to enforce your own bias and viewpoint. These are not news outlets, these are propaganda mills. They are still ideologically censoring certain "major" news issues just to make these scoundrels in the democrat party look less like the scum and America haters they truly are. I make sure they never darken my life or my living room at 5:30.I feel like the proliferation of non standard media (basically everything that is not controlled by the few that ran newspapers and the AP) has caused a "need" to make all mainstream news to be polarizing.
Accuracy and truth are not really needed when shallow reporting backed up by editorials and opinions (which can be woven into the narrative so seamlessly that they are hard to differentiate from facts) are utilized to polarize the masses.
Consider that very few people are actually interested in regular news, mainly because it is either repetitive or boring, or hard to digest due to requiring a wealth of past knowledge to accurately interpret correctly. So it is much better to make the news polarizing, as that way the desired viewership can approach the magic 100%, half of which will believe one way, and half the other.
I use this as an example. My daughter, who is sub high school, knows the names of many politicians. At her age I barely knew the name of the current president. Certainly did not know any senators or reps names. So she has had the dubious benefit of this addition education over what i received. Good or bad, this is the direction that the connectivity of the modern world has given us.
It all goes back to the saying, "there is no such thing as bad publicity". Now these people are making themselves more accessible, using social media to promote their agendas. This broadens their appeal to the ones that agree with them, as well as those that do not. Instead of maybe 10 percent of people knowing who they are, and maybe half of those agreeing with them, they are aiming to get everyone to "tune in" and even if that means that they approach the "magic" 50/50 of love/hate or agree/disagree, they now have orders of magnitude more supporters. I do not believe that this "polarizing" will make any improvements, however I may be wrong.
I am actually stunned they are all still in business!