It's the ol' intentionalism versus functionalism debate which countless historian have studied: most would suggest the moderate functionalism of the holocaust.
People like Goldhaged (extreme intentionalist) are in the mainstay openly rebuked these days because of numerous pieces of evidence suggesting the latter.
You've got Rademacher's Madagascar plan, reports form the Wannsee Conference, numerous orders from the OWK, the Nazi power structure and much more.
Was Hitler an anti-semite? Yes. Did he know of and acknowledge or support the genocide? Undoubtedly. To say it was planned from an early stage? Not for me.
Evidence would in fact point to 1941 being a pivotal point due to many decisions made by Hitler - and importantly others - and as such catalyst for the holocaust.
