but one insidious from

Question

Over the past century,all kinds of unfairness and discrimination have been condemned or made illegal.But one insidious form continues to thrive:alphabetism.This,for those as yet unaware of such a disadvantage,refers to discrimination against those whose surnames begin with a letter in the lower half of the alphabet.
This指代什么?those又指代什么?refers to against

Answer 1

this指的是alphabetism,those指的是those people省略了people,后面的定语unaware of such a disadvantage修饰those,表示“对于正如那些还没有意识到这种不利条件的人们”,refer to意思是“指的是”；against后面接人,表示对象,discrimination against歧视（那些人）.
整个一句话,实际上是个,给alphabetism下定义的句子.翻译为：这,（alphabetism）对于那些还没有意识到这种不利条件的人们而言,指的是对于那些以26个英语字母表后半部分字母开头为姓氏的人们的歧视.