Earlier quoted context omitted.
What does homogeneous have to do with prison rehabilitation? I'm not attacking you, genuinely curious.
The unstated argument to all the homogeneity arguments I've come across (intended or not) is: "We are too bigoted for that to work here, we'd never allow the $OUTGROUP to have it that good", with a side-dish of "they'd be bigoted too, if they weren't homogeneous". When laid bare, it's an appeal to ignorance.
Often, you'll hear people say something like, "Norway did X and it works, so we should do X in the U.S." These are typically fairly naive claims. Regardless of the normative dimension of the claim (whether X is worth doing in the U.S. in the first place), there is a non-trivial amount of complexity that is swept under the rug. For instance, NYC has twice the population of Norway. The U.S. really is significantly more demographically diverse than Norway (or, if this claim isn't good, then we can just say they are equally diverse, but at the scale of the U.S. this diversity increases complexity a non-trivial amount). The U.S. has a more fragmented legal system. Etc. Etc. Etc.
If a Martian were asked which nation would be easier to implement new policies in, maintain those policies, and have them bring about the desired end, which do you think they'd choose? I wager they would immediately choose Norway.