You just shifted the goalpost.

Google's going to maintain a root store either way. The parent I replied to was worried that Google becoming a CA would be a power play to eliminate all other CAs and then Google would get out of the business. Apple, Microsoft and Mozilla have the power to drop Google's CA from their root stores and make Google-issued certs worthless on a huge number of devices worldwide, which is how they act as a balance against unilateral moves by Google-the-CA.