I don't think anyone is arguing about the damage of propaganda here. The discussion here is more-or-less Youtube choosing which propaganda it wishes people to see.

To use your idea here - the cognitive biases being exploited are being exploited by youtube itself. In this example, Icke is a relatively divisive character even on the right wing. So it becomes important to ask - of the controversial figures that remain (on both sides) what cognitive biases is Google/Youtube aiming to exploit by allowing them to continue?