1 Dr. Weitbrecht-Rotholz belongs to that school of historians which believes that human nature is not only about as bad as it can be, 

你还是对英语动词不够敏感。你要注意定语从句谓语动词为单数believes, 由此可知which的先行词并不是historians, 而是that school. school在在此为学派，为集体名词，意为：a group of people who share the same opinions, beliefs, or methods。当一个集体名词被用来指不可分割的整体时，谓语动词用单数，人称代词用it指代，关系代词用which。就如同family指具体一个个成员时，谓语动词用复数，人称代词用they, 关系代词用who/whom/whose；而指不可分割的一个整体时,谓语用单数，人称代词用it, 关系代词用which。

2 about 在此= almost

3 be safe of sth. safe不受或没有受到伤害或不良影响。安全的，免于危险的。后接of介词短语作补足语，表示具体危险因素。of为from的意思。

the reader is safer of entertainment in their hands 意为读者读这些作者写的历史书时，较少受到娱乐内容的影响（弯曲历史）。

以下例句中be safe of sth用法与此类似。

I mainly watch documentaries now, if I watch anything, because they are safe of sexual content usually.

Here I was safe of air-attacks.