Roberts means fake Keynesians here ...
> Keynesians have advocated government spending to stimulate bank lending and private sector investment as an alternative to austerity, but Roberts argues that “Keynesian stimulus policies do not work in a predominantly capitalist economy where the profitability of capitalist investment is very low.”
Here's another quote from Roberts ... " Keynes talked about going further, with the ‘socialisation of investment’ as the last resort. But no government of Keynesian persuasion has ever adopted that policy (if it meant taking over capitalist investment with state investment). Indeed, the Wren-Lewis’s of this world never advocate or even mention the idea of the nationalisation or socialisation of capitalist sectors. For them, Keynesian policy is government spending to ‘stimulate demand’."
It is not really Keynesian to focus on stimulation of finance. Real Keynesian policy would not rely on trickle-down, so it is misleading to call what has been done by capitalist governments "Keynesian." Like Marx and Jesus, Keynes would disavow what has been done in his name.