It has been a commonplace among critics that Hughes adopted the classic blues as the primary model for his blues poetry, and that he writes his best blues poetry when he tries least to imitate the folk blues. In this view, Hughes’ attempts to imitate the folk blues are too self-conscious, too determined to romanticize the African American experience, too intent on reproducing what he takes to be the quaint humor and naïve simplicity of the folk blues to be successful.  

But a more realistic view is that by conveying his perceptions as a folk artist ought to—through an accumulation of details over the span of his blues oeuvre, rather than by overloading each poem with quaintness and naivety–Hughes made his most important contributions to the genre.

请问老师，ought to在句中作什么成分？以及句子中破折号是解释说明的用法吗？