Social accountability, for one. Never underestimate shame as a motivating factor for humans. I'm generally in favor of protecting anonymity, so I'm not fully in agreement that this should be a hard requirement for a software project, but I can at least see the appeal of the idea.
Web browsers are also a rare class of software with high complexity and also high privilege (considering the data that typically passes through them), so perhaps higher scrutiny of this class of software is warranted.
