It seems like they're trading one bias for another. I suspect that the population of users likely to disable telemetry have a lot in common with the population of users likely to just stick with Windows 7 and remove the updates that added telemetry collection.
Personally, I'd probably be satisfied if Microsoft gave me the tools to examine the telemetry that my computer wants to send. Not making that available to users makes me feel like they have something to hide.
Yes they're definitely trading one bias for another in this case. Users who value privacy simply won't use Windows 10 to begin with. And you can't collect telemetry data from non-users.
Users who turn off telemetry can still give you one crucial data point: the percentage of users who do care enough about privacy to turn off telemetry. But this data point is something they simply can't capture because of their insistence on making telemetry mandatory. And any future decisions they make with regards to privacy and telemetry usage will now have to be based on speculation instead of hard data.
In addition to biasing their telemetry data to the subset of users who don't care strongly about privacy, this decision also has a real cost in terms of adoption rates, market share, and damage to the goodwill they've slowly built up over the years in other areas. I just can't see why they'd think this is a worthwhile tradeoff.
They already made that trade by allowing enterprise customers to turn it off.
They also tell you exactly what types of data they collect, along with where and how. That's not consistent with wanting to hide the extent of their telemetry.
What they do for enterprise customers is a moot point to me, an individual, when I can't buy an enterprise-edition license from Microsoft.
I've seen hand-wavy explanations, in general terms, of the data collected. I don't want that. I want to see the actual data collected from my specific machine. Even a bullet-point list including items like "total time executing binaries tagged as 'game'" would be preferable.
There are some good examples of the categories of data that they collect and some information about which features, programs, and apps might collect that data. There are examples within the categories, but not an exhaustive list. Maybe there are more complete lists available for each separate feature. I'd be interested in seeing an explanation, collected into one place, of which pieces of data are influenced by which settings, which ones can't be controlled, etc.
Personally, I'd probably be satisfied if Microsoft gave me the tools to examine the telemetry that my computer wants to send. Not making that available to users makes me feel like they have something to hide.