Earlier quoted context omitted.
As ever, this would be a more compelling argument if the state that granted copyright protections also provided meaningful enforcement. Setting copyright up in a way that often makes it prohibitively expensive to enforce through legal means and then objecting when the rights holders attempt to protect their investments through technological measures feels a little hypocritical.
There should be a choice: either the legal system protects your IP (copyright), or you do (DRM). You shouldn't get the benefits of both approaches, because they are mutually exclusive. Material that is protected with DRM has effectively been stolen from the future public domain. At the very least, key escrow should be required before copyright protection is granted.
Legal status and practical enforcement are unrelated issues. You seem to be attempting to conflate them because you just don't like the idea of copyright.
But that's a different issue. In fact it's perfectly consistent to enforce copyright through a combination of DRM and legal challenges.
Legally copyright is the default. Nothing is in the public domain unless it's explicitly handed over to the public domain.
So software items with DRM can't be "stolen from the future public domain" because the DRM is part of the product or item. And it's up to the rights holder to decide whether or not they want to free it. This is a deliberate choice on their part. (It's a little more complex with other content because the content is assumed to have an existence independent of its realisation or distribution model. Not so much with software.)
None of this justifies Adobe's actions, and a class action against Adobe would also be reasonable. (Realistically not likely to succeed - but hardly baseless.)
But it would be an argument about real/assumed/implied breach of contract with buyers/license users, and not over copyright terms or DRM.