This is because in the "U.S.A.", people in all the regions in the U.S.A. historically migrated throughout an "entire land mass" (essentially) ; and this "land mass" tends to be more "homogeneous" (as opposed to "British English" speakers; who speak with different dialects, accents). Note that the United Kingdom, including Great Britain, is further isolated from the U.S.A.—by a huge ocean— than the "relatively more homogeneous physical region"/ and thus the "relatively more linguistic region".
Moderate means D- to take on a serious mode.
The writer used the word 'moderate' to make a comparison between those people who would lead a serious life without any excess with the group of people who would do whatever they wanted to fight against the Black Death.
1. Hurts the person getting bullied (suicide)
2. Can get in trouble with the law (harassment)
3. Can affect the way people think about you
