Social media allowed people to share their views and opinions in a more open way, so people got more exposed to each other. At same time, the modern world brought a sense of frustration and emptiness which got personified in human relationships. Such frustrations were manifestated on political ideologies, which is also a common topic on social medias which cause division.
So I guess social media is just the tool, but the cause of division is deeper than that mechanism.
Fact is that humans hate each other now and avoid having contact the maximum as possible, and that is mainly due to past negative experiences with other people. Anyway, social media can't be blamed for that.
Social divisions exist and the causes are way deeper than social media. But social media can not be completely removed from the equation. It is a tool that influences how people behave. Social media is not simply reflecting the existing frustration in our society; sometimes it can amplify negativity as well. Sometimes algorithms behave in such a way that it pushes emotional and controversial content because it attracts more audience, gives more views, attention and engagement. The people who already have a negative experience of something /situation can easily find thousands of similar opinions on social media that can strengthen their existing negative remarks and they don't want to challenge them. I think just saying that people hate each other is not okay because of the past negative experiences. In today's time, people still cooperate, they also build good relationships, friendships, and help each other and strangers every other day.