When numerous labourers work together side by side, whether in one and the same process, or in different but connected processes, they are said to co-operate, or to work in co-operation… Co-operation ever constitutes the fundamental form of the capitalist mode of production. (Marx, Capital Vol.1, Ch. 13)
I think that what is key to any advocacy of co-operatives as anti- or post-capitalist organisations, is not co-operation in terms of the division and participation of labour, but rather co-ops as a response to capital’s antagonistic relationship between labour and property: democratic control of capital by workers i.e. a ‘commons’.