"What you're forgetting to mention is practically nobody except Angleton believed Golitsyn - the other intelligence agencies couldn't stomach the concept that they had been infiltrated, so they automatically refuted him."
An incorrect assumption. Golitsyn was intially believed, but as his claims and his influence over Angleton grew the more people figured out his ruse. Angleton, under Golitsyn's influence, declared "war" on experienced and loyal intelligence officers. The agency became paralyzed. Golytsin was happy and so were his Soviet masters.
"The ultimate point of Golitsyn's message was that the Soviet Union was stronger than it appeared. The message was not to underestimate the Soviet Union.
Now you tell me why the Soviet Union would want Golitsyn to send that message, implicitly or explicitly?"
Good grief. You cannot figure out why the Soviets would want to appear stronger than they actually were? Come on - think about it again and reform the question.