I think you are missing some necessary historical context to follow along with what they’re saying here. Capitalists (through military, CIA, NATO etc) have routinely engaged in mass killings of communists around the world. One specific instance being the murder of 1 million+ people (communists) in Indonesia between 1965-1966 all organized and funded by the US. There’s a great book about this called The Jakarta Method: Washington’s Anticommunist Crusade and the Mass Murder Program that Shaped Our World that I think everyone who isn’t familiar with the incident should read.

that makes no sense

Cna you show me an example of where capitlaism has worked? The system has failed every time it has been tried. It is so bad that being around it is bad for other systems. If the systems they touch always fair it is time to consider why they are so toxic.