I investigated this further in [Login to see the link]'s specific context by reading Deviantart's ToS.
I stumbled upon something very interesting. Deviantart's ToS appears to outlaw their own behavior while also protecting the copyright of its users/publishers.
The downside is that like all Internet-based businesses, they write one clause into their ToS that makes it all somewhat irrelevant going forward, adding the "once we give you notice, you agree to our new terms if you continue using the service." (this is #3 in their ToS).
However, apart from the issue presented by Deviantart's ability to change ToS at any time, their existing terms do prohibit their actions, from my perspective:
DeviantArt is, unless otherwise stated, the owner of all copyright and data rights in the Service and its contents. Individuals who have posted works to DeviantArt are either the copyright owners of the component parts of that work or are posting the work under license from a copyright owner or his or her agent or otherwise as permitted by law. You may not reproduce, distribute, publicly display or perform, or prepare derivative works based on any of the Content including any such works without the express, written consent of DeviantArt or the appropriate owner of copyright in such works. DeviantArt does not claim ownership rights in your works or other materials posted by you to DeviantArt (Your Content). You agree not to distribute any part of the Service other than Your Content in any medium other than as permitted in these Terms of Service or by use of functions on the Service provided by us. You agree not to alter or modify any part of the Service unless expressly permitted to do so by us or by use of functions on the Service provided by us.
24. Data Scraping & Machine Learning Activities
DeviantArt is a community of creators that invests significant time and resources to protect its users and foster a cooperative and collaborative environment. Out of respect for its users' choices, DeviantArt has developed clear directives to communicate when its users do not consent to their Content being downloaded and used by third parties for the purposes of developing or operating artificial intelligence or other machine learning systems ("Artificial Intelligence Purposes"). Unless you actively give your consent, for Artificial Intelligence Purposes, DeviantArt will include a robots meta tag with the "noai" or "noimageai" directive in the head section of the HTML page associated with that Content on the Site, and will include an X-Robots-Tag HTTP response header with the "noai" directive when media files associated with that Content are downloaded from the Service. DeviantArt encourages adoption of these directives across other creative platforms, so that creators are able to share their artistic creations with online audiences without fear of losing control of their own works.
DeviantArt expects all users accessing the Service or the Site to respect creators' choices about the acceptable use of their Content, including for Artificial Intelligence Purposes. When a DeviantArt user does not consent to third party use of their Content for Artificial Intelligence Purposes, other users of the Service and third parties accessing the Site are prohibited from using such Content (labeled as "noai" and/or "noimageai") (i) to train an artificial intelligence system, (ii) as input into any previously trained artificial intelligence system, or (iii) to make available any derivative copy unless usage of that copy is subject to conditions at least as restrictive as those set out here. Automated systems or users that fail to respect these choices will be considered to have breached these Terms.
DeviantArt provides no guarantees that "noai" or "noimageai" directives will be present each time Content is accessed, even if the creator does not consent to use of that Content for Artificial Intelligence Purposes; and absence of such directives does not imply creator consent has been granted.
Users acknowledge that by uploading Content to DeviantArt, third-parties may scrape or otherwise use their works without permission. DeviantArt provides no guarantees that third parties will not include certain Content in external data sources, or otherwise use a creator's work for Artificial Intelligence Purposes, even when such directives are present. By prohibiting such conduct, DeviantArt makes no guarantees that it will pursue each unauthorized use of the Service, and the owners of the works are responsible for policing their own works to the extent permitted by law.