These addresses can be used for other, much more terrible things. I do not think it is right to sell them, first you have no consent of the owners to do, and second, create a dangerous precedent.
Anything can be used for "much more terrible things," including crypto currencies as a whole may I add, but each is responsible for their own actions. I have consent of everyone who signed up to my mailing list as it was done through Mailchimp ( user had to sign up + verify email + agree that they were agreeing to opt in). This is completely fine as long as the option to opt out is included by whoever may purchase this in the future.