Why did kennan believe that “threats or blustering” would be ineffective in stopping soviet aggression?

Because the Soviet Union wasn't shy about losses. Threatened with what? Short of global thermo-nuclear war, what haven't they been through?

Threatening the Soviet Union was like waking a tiger...it just ends in pain.

The "threats or blustering" would create more anger, and maybe cause a war or a revolt which is not part of the plan he want to create with the Soviet Union.

They had more africans americans than any other state

Assemblies do not have written codes of laws. laws are matters for magistrates and courts, not assemblies. codes of law are things such as civil law, criminal law, and constitutional law. what assemblies have are procedures regarding debating, voting and other business they might carry out.  also note that rome had three assemblies: the assembly of the soldiers, the assembly of the tribes, and the plebeian councils.