Just because it's optional,
It does not give them the right to break laws wherever or whenever they like.
Say. for example, you decided to sign up to "Damage Inc Social Network", and buried deep within the T&C's of the site, I reserved the right to come around to your house and give you a liberal dose of prison sex while you slept. Now, just because you did a click-through of the T&C's and didn't actually read it, it does not mean I actually have the legal right to break into your house and sodomise you roughly whilst you sleep.
If the region in which you live/login from allows such activities, then all well and good for me, but not so good for you.
If where you live would consider my actions to be breaking and entering (both of your house, and your sphincter), then I deserve to be punished for my transgressions.
Furthermore, any changes to the privacy policies should be made aware to the end user prior to the rollover date, so they have the opportunity to delete all of their content and stop using the service. The fact these things are pushed through without warning, often with the blurb "continued use of this service indicates acceptance of the changes", means people are given no choice but to "agree" if they want to be able to either delete, or backup, the data they have stored.