Existence ≠ Notability := Bad editing experience.
The notability policy has a very practical application: discouraging people to write their CVs on Wikipedia. If there were no notability requirement, I would like to have an Wikipedia article all about myself. This would make me proud to be the subject of an encyclopedic article. And like me there are perhaps millions.
Well, I'm not convinced that we don't already have some form of CV-space on wikipedia - actually every registered editor has a user page, as well as a talk page.
The point I was making is that notability as a reason for exclusion is a great way to upset a lot of people who enter into the WP world. Actually, the requirement for RS as well as an avoidance of COI should be enough to prevent self-authored vanity WP Pages.
Likewise, I know of plenty of people who do indeed have WP pages. Lots of publishers now actively encourage new authors to generate a WP page - the publications model that WP is currently obsessed by implicitly encourages such activity.