I've been reminded of a 1999 book Pre-Code Hollywood: Sex, Immorality, and Insurrection in American Cinema, 1930-1934 that I want to recommend. Before reading this book, I had heard of the "Hollywood production code", but didn't really get the extent of the real honest-to-god censorship that fell on the movie industry for over a quarter century. Basically, the Catholic church set the standards for not just language but topics and plot turns that were acceptable.
Doherty's book brings this out by examination of the several years before the production code went into effect, and before it was actually enforced. The Marx Brothers probably simply could not have made Duck Soup five years later.
In this telling of the story, the production code was largely discredited as an effective and enforceable code by the brazen disregard of... Alfred Hitchcock. I don't know if the destruction of this stupid production code nonsense could really be put down to ONE film; that sounds too romantic and cool to be true.
Doherty makes a pretty compelling case that the movie Psycho specifically and egregiously flaunted the production code. He details the ways. Hitchcock and this movie were simply too big to stop. From there, the decline of the Motion Picture Production Code was rapid.
Dang, Psycho was already the shiznit, but looking at it after reading this book, having some idea of the historical significance of the movie politically- that makes it that much sweeter.
Reading this book will also give you better appreciation for the early work of James Cagney, particularly The Public Enemy, and what a truly raw and risque piece of work that was.