I know it always supports big business. And it’s a reactionary force that people in power turn to when things go badly for the workers and they think of revolt.
But fascism also demands genocide and killing of millions of people and that would only hurt the capitalists, no? Because these are people who would otherwise be working and increasing profit used to increase productivity etc etc etc. But if you kill them you reduce the labor force and thus drive up the price of labor, reducing your profits, and thus what you can spend on improving productivity? And other countries which didn’t do so would become more advanced, leaving you behind.
Don't forget the very real role that slavery plays in fascism. The total violent subjugation of workers to reduce wages to at or below subsistence. For a period, this generates super profits at the expense of maintaining a powerful gendarmerie/police force, but over time it erodes the productive capacity of the nation.
This is one of the real ways in which Fascism "consumes itself". By liquidating large portions of the labor pool for immediate profit and for the purpose of disarming and destroying worker power.