The main problem with these "Pre-Code" festivals is that most of the pre-Code movies aren't very good. We're not talking here about movies from the silent era (which tended, with some exceptions, to be pretty clean); they're all from the early '30s, from about 1930 to 1934, the year the studios finally started enforcing the Code. This was the period when the studios were adjusting to the sound era, trying to come up with a new set of rules for writing, shooting, and scoring films with dialogue in them. And that meant that many if not most of the movies from this era are kind of techincally inept: static camerawork, overly talky scripts, actors straining to be heard by the microphone, no music on the soundtrack (until King Kong the studios tended to assume that a sound movie doesn't need music, a grievous miscalculation that hobbles such movies as Frankenstein and The Public Enemy). So with the exception of a few films, usually from Paramount or MGM, the fun of watching an Old Hollywood movie with "grown-up" content is often compromised by the fact that the movies themselves look so primitive, compared to the technical proficiency of the silent era or the post-1935 era.
It's not necessarily a coincidence that the most adult content in Old Hollywood movies is to be found in Old Hollywood's most techincally inept period (until the collapse of the studio system, that is). Movies were in a period of adjustment. Sound had forced filmmakers to re-learn everything they knew about how to make an effective movie; the influx of dialogue writers, who mostly came from New York, brought a more hard-edged sensibility to Hollywood movies. The studios were often dominated, in that period, by people who were quite highbrow or had highbrow aspirations: Irving Thalberg had some of the most highbrow tastes of any studio head (he once tried to get Arnold Schoenberg to write a score for him); Paramount went all-out for sophistication and urban chic. Under these influences, films were becoming less of a family-entertainment medium and more of an alternative to more family-oriented media, like radio.
The problem with this approach was that movies had become the true mass medium, the thing that everybody, across the entire huge United States, could enjoy at roughly the same time and talk about the next day. And that meant that the more Hollywood played to the urban centres, the more they were in danger of losing Middle America, the rural areas, the squeamish-American community, whatever. It wasn't like today, when niche marketing is in and a movie can be targeted solely to urbanites or teenagers or just some particular group. The Hollywood studios in the '30s had to make movies that had broad appeal across a gigantic country; without that, you got (to skip ahead a few years), something like Citizen Kane which was beloved in the cities and openly despised everywhere else (a magazine rounded up some notes from Midwestern exhibitors who showed Kane: it bombed at every one of 'em). So with that pressure, and with the high-profile failures of many of the "sophisticated" pre-Code movies, the studios started to move more and more toward making movies for everybody, and part of that was making sure that movies would not offend anybody. Another part of it was polishing the technique of movies until they were wonderful to look at. So the increasing technical finesse of movies in the mid-'30s is, in a way, part of the same process that led to the enforcement of the Code: the process of making movies that would be fun for absolutely everyone.
New York plays could use words like "son of a bitch" becaue they were for urbanites, plus the occasional tourist. Hollywood movies were not just playing in Los Angeles, they were playing everywhere, including places that would refuse to book a movie that offended its audiences' community standards. Hence the enforcement of the Production Code: ridiculous, arbitrary, but a necessary tool to make sure that movies would remain a true mass medium. Once the audience started to fragment, and there was no longer a common popular culture -- a process that you can see developing, say, in the '50s, with the huge splits in popular music -- it once again became possible to make movies for the cities, or for the sticks, or for kids, or for non-squeamish adults; to make movies for somebody rather than everybody. At that point the Code was no longer needed, and it accordingly started to crumble away, collapsing entirely by the mid-'60s, by which time nobody assumed that you could sell anything, even a movie, to the entire country.
Tom Sutpen, who posts on rec.arts.movies.past-films, had a good post on L.B. Mayer's role in Code enforcement, which I will quote from here:
Louis B. Mayer's greatest sin (sorry for writing a mini-essay here) was
that he figured out a way to make Production Code enforcement pay off. In big
numbers. Before Mayer took total control of MGM, most studios were loath to
enforce the Code because they all knew it was a money loser of the first rank.
Nobody in the major cities wanted to see the kinds of movies that would result
from the Code; they wanted to see pictures like "Baby Face" and "Midnight Mary"
and "Five Star Final". Who wouldn't?
Mayer, that's who. He wanted 'clean' pictures, and he resolved to make
them, now that he was in charge. He unwittingly tapped into the tastes and
desires of the country's mid-section. They wanted what he wanted: Movies that
made you feel good without having to be good.
Every other studio followed suit and American movies suffered a good three
decades of arrested development in the process.
One other thing is that the vaunted sexual frankness of pre-Code movies somehow never comes off as all that appealing; the slinky, lingerie-clad women of the early '30s may get to sleep around without getting killed for it, but they are not usually very strong characters, defined as they are by their sexuality alone (and besides, they spend so much time in silken pajamas that they never get out and do anything). The silent era and the post-Code era produced much better roles for women, sexually repressed or not.