If you read the thread you'll note that this policy has been around for a long time (at least the ~7 years I've been with Google). The author also notes that, in terms of open source, things have become dramatically _more_ permissive over time.
In case anyone else is unfamiliar with this term.
Employment often imposes lots of restrictions on the actions we can take. I'm fortunate enough to have some choice in the set of restrictions I have to live with, so for me this particular restriction is just part of the deal.
No you don't. You could roll the dice on a legal battle, relying on your employment contract's exact terms in combination with federal & state laws. Like you have to do most everywhere else.
The reason to go through things like IARC is so that you can avoid all of that. It's Google up-front waiving a legal pursuit on the topic, saying "yes all parties agree this is fine."