 One rather extreme answer would be: “not at all”. This hardline view would hold that manipulation is always morally wrong, no matter what the consequences. Inasmuch as this hardline view resembles Kant’s notorious hardline position that lying is always wrong, one might look to Kant’s ethics for considerations to support it. But just as hardly anyone accepts Kant’s hardline position against lying, the hardline view against manipulation also seems short on defenders.