Well there's also the point that USA used Kurds as pawns and cannon fodder. Highly efficient pawns, but pawns nonetheless. USA then tricked them to fall back from more defensible positions with assurances that they guarantee that no harm would come from it while they negotiate with Turkey. Then suddenly USA gave Turkey green light for the slaughter to start. Even if you don't give a flying fuck about the lives of those Kurds, this will probably have detrimental effect on future alliances USA might wanna establish. Reputation for trustworthiness is hard to establish but can be lost in an instant.