People are anti-capitalist because they're increasingly realizing that it's an abominable system that's based on mass exploitation of the working class by people who own capital, and it produces oligarchical political systems such as seen in US and many other western countries that tantamount to living under the dictatorship of capitalists.

Capitalism is responsible for some of the worst atrocities in human history including things like the African slave trade, barbarism associated with colonization of America, countless famines such as the Irish and Indian famines, and never ending wars.

Today, capitalist need for growth and consumerism is literally destroying our very habitat that we all depend on at a planetary scale. Either capitalism ends or humanity will end.