Automation tests are as much code as the code they're testing.
Moving fast and breaking stuff is OK if you're building a web service that doesn't really matter. If Facebook falls over, the productivity at a significant number of businesses probably goes up.
On the other hand, if yesterday's OS security patch stops everyone's PC from booting this morning, or if a new version of your e-mail server has a glitch that means half your company can't log in to read their mail or even that important messages from customers are actually being lost, that probably comes with a cost measured in large numbers of dollars per minute at a medium-sized business, or if you prefer, in careers per hour within the IT group.
Ideally you'd get both engineers writing tests for their code as well QA teams for products.
Indeed, but there is also a good reason that professional editors have new writing proofread or even technically reviewed by people other than the original author.
Maybe there's some subtlety that I'm not picking up here about Microsoft's previous set-up and/or the model they've been moving to under Nadella's leadership. We seem to have some past and present Microsoft developers around these parts, so perhaps their comments will clarify this. But as reported, this looks to me like a retrograde step, an attempt to be more agile and fast-moving rather than something likely to improve the quality of the finished product.
basically the idea is to split the SDET role into two - SE testing (closer to the code than SDETs used to be) and "quality" (further from the code than SDETs used to be). SDET testing, though not directly driven by the code structure, tended to be at a pretty low level driven by a detailed functional spec.