Tish, I think your right to the point of which JK showed the magical population from Harry's perspective, it was not that pureblood's wanted to keep magic in their own families, that is purely a choice matter, but they wanted to eradicate all other types of magic in people of halfblood and muggleborn decendence. In this, she added a dimension to her story the younger readers wouldn't understand. She added race and descrimination.

By separating magic, muggle and creature she gave the book a more realistic perspective. Pureblood's can be in some ways related to people of white skin in Australia (as an example) where the Aboriginal's were attempted to be 'bred out' to create white children and not half-casts or fully indigenous children. But with magic, in appears sporadically as with muggleborn children. It's not genetics anymore, it's chance.

JKR showed this again with the elves. Most or all of the magical population viewed house elves as a class beneath them. When JKR introduced SPEW she wanted to portray subtely her view of the races in a less controversial or derogatory way. The elves however. liked their lives and in most houses were treated with a respect almost equal to a family pet or caregiver. Malfoy's home was an exception, or more probably his character's flaws.

In answer to your question, she captured real life perfectly but by putting it in her story, and watching the world from Harry's perspective it was most probably quite a realistic and just response.