If one wishes simply to utilise some key facets of a particular period, be it 1930s gangsters, then one needn't concern themselves too heavily with societal mores outside of those explored by that particular genre; in this case, alcohol, corruption, organised crime, and the like. Other matters less consequential to the stories you desire to tell can be left to the wayside as needed.
These sorts of games would, given their historical vagueness, would enable more 'modern' social mores to come into play with the PCs as they wish, and it should be heavily noted where historical reality ends and where fictional handwavey history begins. Historical organised crime, fantasy-style race relations for instance.