When you install Windows 10 onto a child's computer, or add a child account to your own PC, Microsoft turns on its Family Accounts feature by default. This safety feature monitors the accounts of your children and reports on their activity. Previously in Windows 8.x it was an opt-in feature, now it is opt out.
Stupid people are complaining about this. And certain websites are trying to make an issue of it.
With the dangers of cyber bullying, websites promoting extremism, violence, self-harm and stalking of children online by dangerous individuals no parent should be allowing their children to access the web completely unsupervised. For all the trust you put in your children there is no 100% safe path and without any intention on their behalf trouble can come looking for them..
By enabling this feature as a default Microsoft is ensuring that all families gain some measure of protection, even those lacking even the most basic technical knowledge. For those who don't wish to track their children's activity on the internet turning off the feature is easily achieved by following a link in the email.
This is one of those features that absolutely should be fail safe, and Microsoft has made the right decision here.