You get Eich 'proclaimed evil' from the section title "The Hateful Browser"? If I hate smoking and contribute to anti-smoking campaigns, am I also evil? FDR hated war - did that make him evil? I know someone who hates her birth father and does not associate with him.
You see where I'm going right? Just because someone feels hatred doesn't mean that the person who hates is evil. Nor that the browser is evil.
The disbelieving "okay Brendan" occurs after giving a direct rebuttal to Eich's second point.
It highlights how the argument "the donation does not in itself constitute evidence of animosity" is incomplete, because the action does not stop at the donation.
Eich knows this, hence using the phrase "in itself" to, as you write, '[tell] you the appropriate lense through which to view the entirety of the content'.
As Davenport (correctly, IMO) characterizes it: "he silently donated to causes seeking to strip rights from minority groups instead of directly harassing them".
Or, as Lehrer characterizes the von Braun defense: "Once the rockets are up / Who cares where they come down? / That's not my department".
Again, how would answer the question "Why was appointing Eich as CEO [of Mozilla Corporation] so controversial?"