My concern: Do I need to have a RealID, or can I just avoid it and accept I cannot use it or the forums?
Remember: Once they have your info, you have no control over it. Their privacy policy might be acceptable today, but that could always change on a dime. What if they decide it is not at all optional? Unless you've managed to avoid ever supplying your information, you'll be SOL. Sure, they might allow opting out of battle.net and everything else somehow and they might even send a notice of the policy change to your email, but the damage might be done by the time you notice and can do something about it. They might not even allow opting out until the change has taken place, it is all in their hands.
No matter what their policy technically is at the moment, the decision to allow them unrestricted control of your information is made at the time of submitting said information and not a second later. It is not made at policy change, nor is it made the next time you use their service.
Overreacting, seriously.
Cars are not out to get me. Drivers are pretty nice where I am. I could probably cross the road a hundred time against the light and not get hit, easily. Doesn't stop me from being cautious. I also have a paper shredder, despite it being unlikely that my ID will be stolen no matter how many sensitive documents I throw away intact. It is not overreacting, it is being a sensible adult instead of an 'invincible' teenager.