Miss Lissy, it depends what the witch wizard thought the worth of the creature. Hermione with her SPEW believed every living creature should be treated with respect. However for some the question is which animal do they feel is more significant, and thats how creatures get there status in the world and this even changes over time. Hermione I believe got it right, treat every living creature wit respect.

On you're pureblood bit it is likes kings of olden times, no one gives them the right to rule anymore just because of there bloodline, however some are still highly respected like in England. But overall as time progressed in the wizarding and muggle societies we both saw it fit to choose governmental positions by ability, not blood status.