An outsider would assume that Sirius's mother cared more about the reputation of the Black family than the well being of her eldest son, but it was the opposite to Walburga Black. Her concerns were equally distributed between the two - the Black family's reputation and Sirius's future. She saw a reckless, rebellious boy upending generations of traditions and trampling on the values that extended back eons ago, her own flesh and blood betraying the values she cherished, diluting purity, and tainting it with the blood of muggles.

To members of the pureblood community, Sirius's rebellion was a symptom of the cancer that was eroding magical prowess in the world and had to be cut before it advanced to the heart of the magical community.

Walburga intended to salvage what remained of that cancer that was her child before he destroyed his bloodline.

Many purebloods shared her opinions, fearing that tolerance towards mudbloods would plunge the Wizarding World into a future of magical desolation, where wizards were muggles and nothing more.