A slight branding dilution in an area that very few users look at or pay attention to that represents maybe 2% of the screen real estate and smallest font when

A slight branding dilution in an area that very few users look at or pay attention to that represents maybe 2% of the screen real estate and smallest font when a user is on your site outweighs the benefit of being able to use a regular CNAME for increased flexibility and scope your cookies to your actual website leaving subdomains available for purposes that would not be viable security-wise if you are using the root domain? Sorry but such a blanket statement is naive and arrogant—you've got to look at individual use cases before making a call on this.