In context, Buckley is linking the misquote of King to another quote about facism at the convention. Its not just a typo, as the whole passage doesn’t work with the word “racist”.
True (I couldn’t see the whole passage), but it doesn’t necessarily imply that Buckley purposely changed the quote.
It would be much easier to figure out what Buckley was doing or trying to do if we had a fuller quote. Does anyone know what the context is here? All I can find is this (added to the quote in the OP):
“…bless him. He says, ‘I would say that I now believe I know how it felt to be a Jew in Hitler’s Germany.’ That is telling it, eh? And what about Martin Luther King? Here he is: ‘Goldwater articulates a philosophy which gives aid and comfort to the fascists.’”
The book was written in 1990. Was the OP the only one to see this in all these years? I could see Gore Vidal checking his work with a microscope to see if there are any mistakes. Or purposely refusing to read a word. Either way actually seems plausible. But I would think someone was looking. And maybe was able to ask him while he was alive.
The problem I have with Goldwater’s principles is the same problem I have with so many other politicians of his era: they only saw white people as real Americans who had rights. They were staunch in their defense of the rights of white Americans but blind to the fact that millions of black Americans were being denied their rights. That was what Martin Luther King and the civil rights movement did - they made white America see black America.
This blindness is especially egregious in Goldwater’s case because he said America had an obligation to free people who were living under communist rule. I can’t agree with an American politician who believed there was an obligation to free oppressed people in Poland and Hungary but no obligation to free oppressed people in Alabama and Mississippi.
On purpose or not on purpose, I just think it’s another interesting example of Buckley being a pyromaniac in a field of straw men 
Buckley was a fascist himself, wasn’t he?
How can you tell when a Conservative is lying? When his mouth is open.