Without fail the information that supports the argument is cherry-picked and that which doesn't is omitted. There are almost always half right and half wrong. 

【翻译】毫无疑问，支持该论点的数据被精心挑选出来，而不支持（该论点）的数据则被省略。几乎总是有一半对一半错。

网友断句失误，句子没错。不要把 doesn't 跟 is 混在一起！

1. that 是个替代词，替代前文的 the information。

2. doesn't 后面承前省略了重复的成分：support the argument。

3. that which doesn't is omitted 完整的表达是：

the information which doesn't support the argument is omitted

划线部分是定语从句。去掉定语从句后，句子完整。