Blood purity

The longstanding separation between the wizarding and Muggle worlds in the Harry Potter universe has led many wizards to advocate keeping the two apart. This view has in turn led to a minority of wizards seeing Muggles (and wizards of pure Muggle parentage) as untrustworthy, foolish, or, in extreme cases, racially inferior. The common practice of wizards marrying Muggles is viewed by such extremists as miscegenation, and they instead advocate maintaining a so-called "purity of blood

http://en.wikipedia.org/wiki/Blood_purity_(Harry_Potter)#Blood_purity
Tweet