That article seems positively rife with weird assumptions, all to present email marketing in a favorable light. It's bad enough that I don't really trust the quote you gave from it.
> Because several of these constraints have been remedied over the years, many of the concerns that users had about subscribing have disappeared.
Read: Because we stopped asking permission and instead started spamming everybody who gave us their email address, people stopped thinking that not subscribing had any effect.
> The increase in sheer email volume over the years has created a scenario where people can’t possibly give all messages their full attention, so they care less about what they receive because they know they can easily ignore the noise or choose what they invest their time in.
Read: Our entire industry spams people so much that people know it's not worth reading.
> It’s no longer used strictly to describe unsolicited email messages. Participants in our study used the word “spam” to describe solicited marketing emails that they considered random, impersonal, irrelevant, with too much promotional hype, or coming in high volume.
Read: We required an email address for things that don't need one, then treated that as permission. How dare people consider our spam to be spam?
> Now that organizations are required to include an Unsubscribe link in their newsletters, this task has become easier.
If a company assumes that an email address given for identification can be used for marketing, or that it can be shared with third-parties/affiliates for marketing, then they are already pretty shady. I honestly have no way of knowing whether it's an actual Unsubscribe link, or whether it's a signal that the email address is actively read by a human and so should receive more spam.
> If users keep getting unwanted newsletters, the messages will start to backfire and become regular reminders that they’re annoyed with your company. Better to let them go.
This part I do agree with. Better still would be to not assume permission to send marketing to somebody just because there was a pre-checked both on a form.