Corporations being "fictive person" (whatever that means) isn't a relevant factor. What does matter is that they are legal persons[1], and therefore can sue people under tort law. It's not hard to find defamation cases where corporations are the plaintiffs[2]. In fact corporations suing people for defamation is such a big issue that there's even legislation to prevent it from being abused[3]
Yes, 'legal person', as opposed to real or physical person, i.e. a fictive person.
In the US, can other fictive persons sue for defamation too? If I walk around in a US city with a sign claiming that Barney the dinosaur stole diapers from orphans and use hard drugs, is that legally defamation? Or is it restricted to fictions used to name and organise economic activity, is it money and bookkeeping that creates this particular personhood?
> Yes, 'legal person', as opposed to real or physical person, i.e. a fictive person.
>In the US, can other fictive persons sue for defamation too?
The case law is pretty clear that yes, corporations can sue for defamation. As I mentioned before, you can find plenty of appellate-level cases where corporations have sued others for defamation. The fact that nobody has seriously tried to have such cases quashed on account of "corporations are fictive persons" or whatever suggests that it's not a serious legal argument worth considering. Arguing over this makes as much sense as arguing whether driving a car counts as "traveling" and whether that's protected by the constitution or not[1].
If you think it's fine and dandy that fictions are treated as if they're real in courts, that's just like your opinion, man.
Where I live, fictions aren't treated that way. The closest thing we have is immaterial rights, copyright and the like, 'protecting the fruits of spiritual labour'.