He became so associated with tone clusters that Bela Bartòk wrote to ask his permission in using tone clusters for a string quartet. Why was this necessary? No one wrote Schoenberg asking his permission to write serial music, or checked with Messiaen before using one of his modes. Perhaps it was a simple courtesy, from one ethnomusicologist/composer to another, but it is certainly an odd story. Plenty of instruments have been patented, but I am not aware of any compositional techniques that have been protected, beyond the refusal of the composer to explain the workings of his/her music. By the way, I just ran across this story about troubles in Cowell's life that I was previously unaware of.
Then in 1936, when he was 39, his life fell apart. Cowell was arrested andcharged with performing oral sodomy on a 17-year-old male. Sweet-tempered and naively honest, Cowell had allowed neighborhood boys to swim in the pond behind his home. Apparently things happened. In his defense, Cowell stated that the boys, the youngest of whom was 16, had been the instigators, and that in no instance did anyone do anything through coercion. The Hearst tabloids seized on the story. Saying he did not want to submit the youths to a trial, Cowell pleaded guilty and was sentenced to prison at San Quentin.
He was shaken but not bitter. In prison, he taught music to some 1,500 inmates, organized an orchestra, composed 50 pieces and wrote a book on melody. Released on parole in 1940, Cowell, with the support of his colleague Percy Grainger, established himself as a composer, teacher and organizer of modern-music events in New York. In 1942, he was granted a full pardon.
But he never shed the humiliation. Some colleagues cut off ties completely. Charles Ives, who had been like a father to him, agreed to see him again only after Cowell had married in 1941.
Fortunately, Cowell did recover from the scandal. The article I quoted suggests that his compositional style changed after this point, contrary to the trends that the author felt were the norm. However, Copland and Harris had just started the populist movement, and it is understandable that fellow American Cowell would come on board.