How not to build a mailing list

I mentioned yesterday one of the major political blogs launched their mailing list yesterday. I pointed out a number of things they did that may cause problems. Today, I discovered another problem.
This particular blog has been around for a long time, probably close to 10 years. It allows anyone to join and create their own blogs and comment with registered users. As part of their new mailing list, they added everyone who has ever registered to their mailing list. They did not send a “we have a new list, want to join it?” email, they added every registered user to the list and said “you can opt out if you want.”
This is such a bad idea. My own account was used once, to make one comment, back in 2005. Yes, 2005. It’s been almost 5 years since I last logged into the site. Sure, I have email addresses that go back that far, but not everyone does. That list is going to be full of problems: dead addresses, spamtraps, duplicates, unengaged and uninterested.
Seriously, they’re adding people who’ve not logged into their site in 5 years to a mailing list. How can this NOT go horribly wrong?
My initial thought was this was going to blow up in a week. I’m now guessing they’ll start seeing delivery problems a lot sooner than that.