This saying is used by people who are anti-capitalist to show their disapproval of Capitalism whos wealth is built on the exploitation of the people - literally to starvation. It is a warning to the rich who would build their wealth at the expense of everyone else, as the poor will unite in arms to take their heads ("eat" here not being used literally to mean cannibalism). Today it is a battlecry or slogan to rally the working class against those that would exploit them. This phrase was used more at the beginning of the 21st century because of increasing income inequality.