If Bellatrix cares about blood purity, why did she destroy the longbottoms?

 Bellatrix Lestrange tortured the Longbottoms, not necessarily destroyed them. She did so to extract information about the whereabouts of Voldemort after his initial downfall. Bellatrix was fiercely loyal to Voldemort and his cause, prioritizing his return over pure-blood ideals in that particular situation.

Bellatrix Lestrange, a fervent supporter of Voldemort and a staunch advocate for pure-blood supremacy, tortured the Longbottoms rather than outright destroying them. The incident in question occurred during the dark days following Voldemort's initial defeat. Driven by her unwavering loyalty to the Dark Lord, Bellatrix sought information from the Longbottoms regarding Voldemort's whereabouts. In this instance, her allegiance to the cause of resurrecting Voldemort temporarily overshadowed her emphasis on blood purity.

It's important to note that Bellatrix's commitment to pure-blood ideals was a central aspect of her character. However, her actions against the Longbottoms underscore the complexity of her allegiance. In that specific circumstance, the urgency of finding Voldemort took precedence over her traditional beliefs. This deviation highlights the extent of Bellatrix's devotion to the Dark Lord, illustrating that even a fervent supporter of blood purity could prioritize the resurrection of Voldemort over adhering strictly to those ideals.

The torture inflicted upon the Longbottoms served as a grim testament to Bellatrix's ruthlessness and the lengths she was willing to go to serve Voldemort. Her actions were not driven by a disregard for blood purity but rather by the immediate necessity of securing the return of the Dark Lord. This incident stands as a poignant example of the intricate interplay between loyalty, ideology, and the pursuit of Voldemort's goals within the dark and complex world of Harry Potter.