Websites like Reddit Profile (https://redditprofile.com/about) and HN Profile (https://hnprofile.com) systematically scans all HN comments and identifies all users' expertise, personal interests, activities and emotions, and allow employers to uncover their E-mails and hire them. And it's just a one-man's startup as a social experiment, larger agencies and corporations have at least many order-of-magnitude higher budgets. And I definitely think not everyone wants that.
The problem, I think, is this type of behavior encourages inappropriate uses and abuses of anonymity.