I'm assuming you're implying that attempting to deny the rights of citizens to use works in the public domain doesn't provide sufficient harm to support a law suit?
In which case I disagree; it is an insidious harm inflicted on the entire citizenship.
The issue isn't that it doesn't indicate harm, and I'm not saying that standing wouldn't permit a suit, but in general, unless the plaintiff can demonstrate to the court direct harm.
If that harm is shared by a large group of persons, any one person may not have standing to demonstrate harm to that group, unless a class action can be brought.
I do entirely agree with your point that this is a harm against, not only the citizenship, but all persons who may lawfully use public domain or otherwise unencumbered works. That's unfortunately not the question addressed by standing, and law (often, though not always) hinges on specifics.
Law isn't my specialty, though I dabble in some research on the topic.
>unless the plaintiff can demonstrate to the court direct harm //
The harm per capita is slight in financial terms I'd agree. But demonstrating the harm is simple - I did something with a PD work, this company acted to prevent my free exercise of using that PD work.
It's akin to blocking a public right of way (not sure about law concerning such things outside the UK sorry) - you block access on a path or road that should be free to access by the public, you're preventing a person from exercising their rights.
Possibly there is a libel issue too - the company [maliciously] claim you're copyright infringing, you show the work used is out of copyright and that the company would have [on the balance of probabilities] known that.
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¹ I gather that's the measure used for torts in the UK courts.
In which case I disagree; it is an insidious harm inflicted on the entire citizenship.