Earlier quoted context omitted.
I don't think anyone is claiming "purity" at all. Purity, if anything, would make things simpler.
The operating principle is homogeneity. Purity is a bit of a misnomer because a "perfectly" homogeneous species with no distinctive heterogeneous groups would have to be called pure, but that's not usually how people use the word. The implication is usually that there are several distinct, homogeneous groups within which there is homogeneity among its members. Having homogeneity at some level, even if it ends up bein…
and yet it is possible we will need to end up where individual advice is the only one working