That is a valid reason, especially to the providers who are forced to deal with the problems and complaints from their customers and others. As an individual not involved in the administration of an ISP my main issue is that of privacy. It is NOT a free advertising medium for advertisers. This is absurd. No one should have to ask to be removed from any list that they did not ask to be included on.
Lets do some math.
There are an estimated 23,000,000 online businesses, not including the kids and individuals operating web pages with banner ads trying to make a few bucks. If 1 in 1000 sent one each month that would average 767 emails per day, and of course 1 in 10,000 would still average 77 emails per day. Even a provider as large as AOL would find it very difficult and expensive to deal with that much additional email traffic. The costs would be passed on to the members in increased membership fees if that were to happen. Which is a moot point because it has already happened to AOL and many others as you will see in the pages to follow.