Capital succeeds because it runs on critique. It produces dissent, and dissent therewith produces more capital. A final stage capitalist society would be entirely leftist & organized around a continual critique of capital.
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Capitalism's driving force is inner contradiction, productive self-negation. 99% of all cultural material produced by capitalism is a critique of capital. Communist art is a critique of systems opposite to itself while capitalism critiques itself and gains plus-value therewithal.
Of course they can't. Liberal democracy (synonym of "forces of capital") tolerates ANYTHING that does not contradict its core principles, namely, free flows. It integrates and internalizes as much dissent as possible, but some has to be cast out as non-recuperable "enemy".