More important, Noah could not CURSE what God had already BLESSED. (Who wins that rouhd?)
Frankly, I have heard that as the reason that Ham was not cursed, but have never understood it.
God establishes a covenant with the sons of Noah not to destroy them again with a flood.
Why could He not have then cursed Ham to be a servant of servants if he were in fact guilty of some crime?
The blessing had nothing to do with the cursing.
That is only used by the sons of Japheth trying to justify their enslaving all the sons of Ham (not just Canaan)