To opt out of mandatory arbitration and retain the right to participate in a class action, the terms of service state:
Your written notification must be mailed to us at Stack Overflow, Attn: Legal Department, 110 William Street, Floor 28, New York, NY 10038 or by email notification at team (at) stackoverflow.com. (…) Such notification must include: (i) your name; (ii) your email address and mailing address; (…)
So we have a choice between waiving legal rights, and revealing our name and address? This is a problem.
I understand why the waiver is based on a name and address rather than an account: it's a legal agreement between the person who has agreed to the terms of service and Stack Exchange, Inc., not a property of the account. However, it is deeply disturbing that one cannot be both anonymous and legally protected.
Please change the terms of service to allow opting out of mandatory arbitration by identifying oneself only as “the owner of Stack Exchange account NNNN”.
(I'm quite willing to believe that you weren't trying to expand your data collection at your expense, you just weren't paying attention. But it's quite a big thing not to pay attention to, and you should not have changed the terms of service until you understood your own terms of service! The current terms of service are strongly Evil. Please fix them before this evil can have concrete consequences, i.e. well within 30 days from the change. Of course, a better fix would be to make arbitration opt-in instead of opt-out, as it is by law in the EU.)