You are wrong on both points, FWIW :) But it's definitely true at other companies.
" And I do see the concern about people being dismissive of others based on their employers, particularly in comments not directly related to the topic being discussed."
Given another person just literally said to me "the opinion is less valuable because you work for X", i'm much more worried about this attitude than i am the one where people are biased towards their companies.
Most people in tech are not true believers. Most probably like their companies. But that doesn't mean they agree with what their companies do all the time. Especially in a company the size of, say, Google, it's pretty, IMHO, silly to think that among 150k of those people, there is no dissent, or not even a lot of dissent, all the time.
Therefore, the participation of employees adds a lean in their favor, and disclosure, if it doesn't neutralize it, at least flags it so people are aware.
Mind you, knowing you're a Googler, I did upvote your original comment, because I thought it was accurate and had value. And I do see the concern about people being dismissive of others based on their employers, particularly in comments not directly related to the topic being discussed. (Imagine trying to comment here with "Uber, Inc." after your name.)