I'm with Pam on this one. Editing and reading are not two halves of the same participation at all - they are distinct activities. There should be no (or at least minimal) barriers to people participating in both but there is a fundamental difference between them.

Reading Wikipedia and other Wikimedia projects is an act of consuming content. With varying degrees of interactivity you can choose which content you want to consume, and in limited ways how you want to consume it. It is possible to read Wikipedia etc in many different environments, for example using a desktop computer, handheld tablet, e-ink reader, dead-tree books even projected onto the side of buildings iirc. The reader has no responsibility to or for the content and enters into no legal agreement with anyone (although they may do so with others in order to access Wikipedia in some modes).

Editing Wikipedia is an inherently interactive process of collaborative production. It entails the responsibility to abide be the legal agreement they enter into, and the requirement to not insert copyright violations, to agree to community norms, and display at least basic competence, etc. Editors must agree to be responsible for the content they enter, and so must be old enough according to one or more legal jurisdictions to assume that responsibility. It is not possible to edit Wikipedia in all modes it is possible to read it in.

Look at attachment 12954 (the second attachment on bug 52004 in case that link doesn't work) for perhaps the clearest evidence about how reading and editing are fundamentally different concepts.

In addition to the above there a practical difference with the way one has to behave with a reading window and editing window. When reading, I can paste a new link anywhere on the page to view a different article, or an can follow a link from anywhere in the page with no need to think about anything else; I can page down using the space bar (often convenient on this laptop), and I can simply type a few characters or words to quickly jump to a different part of the page. When editing I cannot do any of those and I need to be able to tell at a glance whether pressing tab a couple of times followed by enter will take me to the third link or will alter the formatting of the page.