Congress can pass a law requiring opt-in for participation. Right now most providers offer opt-out, only takes a little personal effort to protect your privacy.
I wouldn’t feel overly confident in the measures you’ve taken. If there’s one thing we’ve learned in recent years it’s that it’s not all that hard for people to get through even the best security measures. (Or Wikileaks would be outta business).
But, more to the meat of the matter, this is about people’s privacy. They should have no need to jump through hoops in wild hope of avoiding not having their privacy and personal info made public by an entity to which they’re paying money. Unless the company is a PR firm (and an awful one at that).
We don’t give the USPS the right to make copies of all our incoming and outgoing mail to sell on the street corner. This is just basic common sense. If anything, in an age when attacks on personal privacy are commonplace the goal should be to limit such attacks in any form, not aid and abet them.