Let me ask you this then,
If the Prime Directive is so arrogent, what would have happened if the Spainards use it with the Meso-Americans instead of using the raping, pillaging and 500 years of Catholic guilt and cutlrual assminilation. Would the world be a different place? Would things have turned out as bad?
No one will ever know.
But you're automatically saying that the mistakes we've made before we'll make again. I don't think anyone here is presenting the idea that Starfleet officers raping the natives and giving them blankets infected with small-pox would be allowed.
Plus, in a post-scarcity economy that Trek presents, there would be little of value to be gained from primitive cultures that you help in most cases.