When The Playboy of the Western World was first staged, critical opinion was so violently against it that Yeats came to Synge's rescue by holding a public debate and declaring, in Synge's defense and in a still controversial statement, that
every man has a right to hear [a play] and condemn it if he pleases, but no man has a right to interfere with another man hearing a play and judging for himself.
Yeats' above declaration that the play must go on so each person is free to form their own opinion--be it good or bad--was prompted because viewers and critics alike found the depiction Irish peasant life in Playboy to be an outrage against Irish pride and decorum: Irish people did not so demean themselves in the way the play shows. Viewers and critics also found that Synge's choice of language was vulgar, offensive and an unending, unfounded display of profanities, with the Freeman's journal calling the language, "the elaborate and incessant cursings of [Synge's] repulsive creatures."
The tide has turned however and today critics praise the very qualities that the first critics lambasted. Synge's portrayal of life on the Aran Islands is said to be authentic and realistic while his language is said to be poetic and lyrical all throughout the play.
It is to simple but exotic strains—to the melodies of rustic flute and weatherbeaten strings that the spirit of J. M. Synge is disclosed—the spirit of bogs and peatmarshes, the spirit of unfettered poetry. Wild poetry itself is in his utterance …. [T]he play is full of such lines, and illuminated with the most skilful character-delineation .... (Untermeyer essay)
As social values change and as sensibilities become immune, so to speak, to breaches of previous levels of morality and decency, critical opinion takes a different tack in arriving at an analysis of works, like Playboy, that at one time brought boos and spitting and walk-outs and arrests and public bans. For good or ill, Yeats' opinion has carried the day.