The previous answer set up the historical context for why Stanley would admire the policies of Huey Long. Stanley agrees with the idea that a man should be the master of his own home. Like Long, Stanley casts a critical eye on the wealthy elite class of the south, represented in the character of Blanche, a former wealthy southern belle who now lacks money but more than makes up for that with her sense of class snobbery. She looks down on Stanley and his working class lifestyle, and treats him like an animal.
Additionally, Stanley's tyrannical character resembles the portrait Long's opponents painted of him: as a potential dictator. Long was considered dangerous by some, including writer Sinclair Lewis, who when writing his dystopian novel It Can't Happen Here modeled his villainous fascist politician Buzz Windrip on Long. Whatever one's views on the controversial Long, Stanley is certainly a dictator in his home, dominating his wife and eventually forcing himself on Blanche.
By including real life people in his play, Williams creates a sense of realism in A Streetcar Named Desire. Huey Long, Jr was the mayor of New Orleans from 1928 to 1932. Nicknamed the Kingfish because he thought of himself as a small fish when in DC, but a kingfish for the people in New Orleans. He was charasmatic and loved by his supporters, but charged by his opponents as being a dictator for his swift action. He was assisinated by a political rival's son in law in 1935 at the age of 42.
In Streetcar, Stanley refers to Long by alluding to one of his campaign slogans, "Every man a king." When he tells Blanche and Stella
Who do you two think you are? A pair of Queens? Now just remember what Huey Long said- that 'Every man's a king- and I'm the king around here.
Since Long's policies suggested in changes in financial polices to help those affected by the depression with his "Share the Wealth" program. Stanley is a supporter of these policies and the idea that every man can and should be the king of their own home.