The polarization online reflects the current toxic political and social climate, and vice versa. Add record divorce rates, cratering marriage and birth rates, stir in a bucket of social isolation and you have a recipe for disaster. Intentionally divisive media slants are designed to play into confirmation bias and further polarize society. Whether it's the NRA jacking up their base with fears of government removing guns as a plot to usher in totalitarianism, or feminists and their supporters crying "all men are rapists", the goal is never to further meaningful dialogue and reach consensus. The motive is to extract more money and expand political power. And angry people are the most malleable. The web acts like a huge wind to fan the flames of discontent. Angry people need lots of validation, and the internet provides and ocean of it.
By keeping us disunited, powers that be can get away with a lot of shady stuff that a truly united people would not tolerate.