>>4085091. Almost every intelligence agency on the planet exists to serve capitalism and do everything in their power to undermine leftist movements. Most notably the CIA which has spent decades figuring out ways to infiltrate and subvert left-wing organizations.
2. Right-wingers have massive financial backing and every single prominent right-winger (politician, media figure, or otherwise) is in it for the money. Almost any divisiveness can be solved with enough money. Just look at the 2016 GOP primary, Trump was vicious against Ted Cruz, Marco Rubio, etc yet they fell in line immediately afterwards because they don't have any real pride or principles, they all serve the same masters.
3. People who read a lot, pay attention to the news, care about the issues, etc tend to be VERY opinionated and have a clear understanding of how the world should work. This inevitably leads to friction with other similarly opinionated people.
4. A lack of political victories combined with the world getting noticeable worse year after year has lead to disillusionment and a desire to blame someone or something, resulting in in-fighting. Particularly in the United States whose politics is explicitly designed to keep leftists from gaining power. This is a facet of "cancel culture" as well, basically people will go after those they think can be destroyed, and not those who can't.
5. Social media ruins everything. Twitter is one of the worst places on the internet to have real discussions, just for the character limit alone, yet it has become the center of public discourse. Facebook is a den of nutcases driven by rigged algorithms. YouTube rewards e-celeb drama and demonetizes/shuts down leftists doing actual reporting. etc