"....this is what you really are isn’t it? A murderer, a torturer, a—"
-- Scorpius Malfoy to his father Draco (CC3.3)
In the alternate timeline where Harry Potter lost the Battle of Hogwarts (caused by the use of the Experimental Time Turner), the incarceration of Muggle-borns is sanctioned by the Ministry of Magic (CC3.3).
Reminiscent of the Nazi death camps the "Mudbloods", whose impure blood who might possibly pollute the pure-blood wizard community by intermarriage, are removed from society and killed. J K Rowling is trying to show what would happen in the world if people stand by and allow evil to win.
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About the play: http://www.harrypottertheplay.com