> How so? There are no restrictions on use or distribution.
It's not open source because it does not use an open source license (public domain is not a license). It's not free because this depends on your and the author's jurisdiction (if you both live in the US, then yes there are no restrictions on use or distribution)
> I would include neutering any commercial uses, in which case GPL is non-free.
In what way does GPL neuter commercial uses? GPLv3 simply states that you have to make your code available to your users (note: users, not everyone), not that you cannot sell your product.
Jurisdictions always matter, other OS licenses are also subject to local laws and its not a given they will be valid or interpreted as intended. Arguably it's the intention of the creator of the software that matters in how licenses are actually enforced (or not). So in that sense PD is fine. There are also plenty of easy cures for PD, such as making changes and then copyrighting and licensing that derived work as required.
The GPL forces you to license all your relevant software under restrictive terms (ie under the terms of the GPL). How people can declare that as 'free' I'll never understand, it's just ideological nonsense.
The GPL makes it hard or impossible to make money from your software since anyone else can duplicate and sell it. That's obviously neutering commercial use.
How so? There are no restrictions on use or distribution.
> Restricting commercial use is also not free.
I agree, and I would include neutering any commercial uses, in which case GPL is non-free.