> It is a difficult issue because businesses need to be able to advertise =
> to potential consumers who have e-mail addresses,
 
Ridiculous.  Businesses do not "need" to use e-mail to reach "potential"
consumers.  They do just fine without e-mail.  Their only "need" is to
save a few bucks by having junk mail paid for by the recipient, as in
spamming.
 
There's only one way to be sure that a subscriber wants to be on a list:
advertise the list (not via spamming) and have them subscribe.  There are
far too many idiots out there vacuuming up e-mail addresses and selling
them to other clueless idiots.  If a clueless advertiser hands you a
large list of addresses and tells you to send mail to all these people,
you are spamming, and will be treated accordingly.  Just that simple.