Hollywood, however, became home to many native Southerners, people who might have given Vivien Leigh and Leslie Howard some much needed dialect coaching on the subtleties and diversity of Southern speech. We don't always recognize them as Southerners because success in show business often required the erasure of regional distinctions like accents. Actors from many parts of the world acquired voices to match the industry's homogenized image of Anglo-American whiteness just as they acquired new names and even new biographies. Southern accents were particularly undesirable for leads, since they connoted ignorance and backwardness instead of cosmopolitan sophistication or even all-American integrity. Character actors and comedians could get away with their native dialects to a greater extent, but sometimes they ended up feeding the negative attitudes audiences had toward Southern speech. It was a circular trap well known to actors from any kind of ethnic or racial minority.
Dick Van Dyke's bad attempt at Cockney irks actual Cockneys. For one thing they tend to obliterate all regional variation, and in reality there are as many distinct Southern accents as there are types of BBQ sauce (seriously, we have a lot of types of BBQ sauce, but the only true one ordained by God is mustard-based, and I will fight you to the death in defense of it). Even in 1944 Hollywood knew it wasn't doing right by Southern voices, as this article in The Evening Independent makes clear. The whole thing has the air of a joke, but of assumed Southern accents Tallulah Bankhead is quoted as saying, "I've never heard one on either stage or screen that did justice to southerners." Bette Davis and Henry Fonda try it in Jezebel, Gary Cooper attempts it in Sergeant York, and Leigh does her honey belle thing in both Gone with the Wind and, later, A Streetcar Named Desire, but they all achieve about as much authenticity as a Bugs Bunny cartoon (like this one, which is all kinds of problematic, and I'm warning you now not to read the comment thread.)
Today things are different in the movie industry. Stars like Andy Griffith and Elvis helped to make genuine Southern voices more familiar to viewers, and the modern South shows up a lot more often in films and television shows. Still, our larger cultural sense of the South and its voices remains complicated. It's true that the South can be its own worst enemy in terms of the rest of the country's opinion of it (I'm looking at you, North Carolina and Alabama; you've both been busy lately). However, there are plenty of progressive Southern voices trying to be heard, with or without a "grits-thick" drawl. I have to wonder, when I'm listening for Southern speech in classic films, how those voices are reflecting, obscuring, and shaping a culture's identity. Maybe you will, too, the next time you sit down to Show Boat or Tobacco Road.
If you're really curious, you can hear my voice on this episode of BBC Radio's Last Word, where I'm talking about Jane Henson. My segment starts around 22.08 minutes into the broadcast.