> The controller shall implement appropriate technical and organisational measures for ensuring that, by default, only personal data which are necessary for each specific purpose of the processing are processed. That obligation applies to the amount of personal data collected, the extent of their processing, the period of their storage and their accessibility. In particular, such measures shall ensure that by default personal data are not made accessible without the individual’s intervention to an indefinite number of natural persons.
The intent appears to be to prevent a scenario where personal data is "shared publicly" by default. Given the broad definition of "personal data" and the underlying principle of "privacy by default", it seems likely to me that a "default-to-public" sharing system would be non-compliant.
I don't really understand why services like these don't drop the pretense of keeping your private data private, and instead simply say "anything you write on our website will be published online publicly".
While there might be some user backlash, I don't think it would be that big, and would meet all the laws and regulations.