The way the Marxist argument for class interest works, is that there does not need to be a secret cabal. To discuss this in the context of basic income (BI): Some capitalists, that is some owners of capital, depend on cheap unskilled labor. Each of them concludes independently, that a BI is against his own interests, since it would reduce the incentive to take unpleasant jobs and force them to pay their workers more.
Or more generally, some people have similar interests, not because they conspire, but because they are in a similar socio-economic situation. And this socio-economic situation generates class interests. ( Marx then goes on to argue, that the capitalist class can more easily leverage its interests, and therefore the workers need class conscious to counter this leverage.)