Over on Deliverability.com Krzysztof posts about discussions going on over on the URIBL list about using “confirmed opt-in” to describe a subscription process versus using “double opt-in” to describe the same subscription process. I do not even need to read the list to know what is being said. This is a disagreement that has been going on since the first usage of “double opt-in” over 10 years ago.
To better explain the vitriol, a little history of the two terms might help.
My personal recollection and experience is that the term “confirmed opt-in” was coined by posters in the newsgroup news.admin.net-abuse.email around 1997 or 1998. There was some discussion about marketers / spammers (a lot of the posters did not distinguish between the two) trying to use the term “double opt-in” instead of “confirmed opt-in.” Many posters believed (and many still do) that this was a deliberate attempt by marketers to make the process seem overly burdensome and unworkable.
During the 2003 FTC spam hearings, Rebecca Lieb shared formal definitions for 5 different subscription types including “Confirmed opt-in” and “double opt-in”. These definitions are still up on ClickZ.

Confirmed Opt-In
[…]confirmed opt-in lists confirm, by email, your subscription as soon as your name has been added to the list. They allow you to unsubscribe immediately by replying or clicking on a link within the email. […]
Double Opt-In
A double opt-in list means not only must the user take an action to add himself to a list, but he then receives a confirmation of his subscription. He must reply to be added to the list. […]

What we have here are two terms describing the same process and two different processes being described by the same term. Not only that, but the term describing two processes is also one of the terms terms used to describe the single process. I am confused just trying to describe the situation.
Adding drama to the confusion, there are some people who believe very strongly that marketers specifically published different definitions of confirmed opt-in to confuse discussions with anti-spammers. Whether or not this was a deliberate decision by marketers, the reality is that it has set the stage for years and years of confusion, obfuscation and controversy.
This is something I deal with on a regular basis. In order to make things clear with clients, ISPs and blocklists I cannot just use a term and be sure we all agree on what that term means. Instead, I have to define terms at the beginning of the conversation and make sure that everyone involved is using the same terminology.
So what happened on the URIBL list? Al answers that question at SpamResource.

Some random guy, nobody I know, he posted a request for help. He said, more or less: “Hey, blacklist XYZ has listed my double opt-in server. What should I do?”
Approximately 13 seconds after posting, he was verbally attacked in response. He was accused of being a spammer, and ridiculed, for daring to use such a term as “double opt-in.”
[…] a discussion forum made up of supposed thought leaders, people who actively work to stop spam, accused the guy of being a spammer. They didn’t accuse him of being a spammer because he sends spam — but instead, they called him a spammer because he used a term that they do not like.

There are anti-spam groups and people running blocklists who still treat the term “double opt-in” as a sort of reverse-shibboleth. People who use the term double opt-in, are not a member of the anti-spam community, and are unwelcome and shunned. Even those of us who have been around for many, many years are treated as outsiders and spammers if we accidentally use the wrong terminology in front of anti-spammers.
There is no solution I can see. The confusing terminology has been around long enough that there is no way to clarify things. Inventing new terminology is only going to increase confusion. Expecting either marketers or anti-spammers to abandon “their” terminology is patently ridiculous. The best those of us trying to deal with both groups can do is to be bilingual.

anti-spammers • Definitions