In his review of The Ominous Parallels, Dr. David Gordon points out that Leonard Peikoff is not reliable when it comes to intellectual history. Gordon reviewed OPAR and commenting on the mistakes in that book said "The author of The Ominous Parallels has not lost his technique." One of these mistakes was the attribution of the famous phrase "we are all socialists now" to J.S. Mill.
Well, I'm up to session 9 of the DIM lectures and what does Peikoff say? You guessed it. "Mill said we are all socialists now."