Ashley Jester, in a must-read in Commonplace:

When a deal is struck that covers some or all of the APCs, that deal explicitly validates the idea that APCs are an appropriate part of the open access ecosystem.  You are no longer arguing about whether or not individual authors should have to pay to publish their work openly but are merely haggling over the terms. 

The essay makes a lucid case that read-and-publish deals—like the one that UC struck with Elsevier, or the slew of recent Cambridge agreements—are lowering barriers to readers by raising them for authors. Read-and-publish deals look they’re building a public good, but they’re actually more like Gramercy Park—a deal-by-deal club good for those who can afford to author.