As now everyone will rush to copyright "common" API signatures, and lawsuit troll anyone found in violation of the copyright?
"I see your FOSS uses `parse(string)`. We own the copyright on that API, please buy a license or we'll sue."
So then every API would become i.e. `umvi_parse(string)` to avoid paying. I'm sure all sorts of auto-prefixer tools would pop up to help automate this, but still...
The Oracle argument (and as things currently stand in their case, the accepted argument) is basically that the API taken as a whole can be protected even if each individual function name can't, so you could protect the "Java API" but not "compare(a, b)". The idea of copyright arising from "structure, sequence and organization" is well established in the computing context as well as others (for example, you can hold copyright in a compilation even if the individual things being compiled aren't themselves copyrightable).
Still, API copyright would lead to all sorts of uncertainty at least at first, and certainly puts compatible implementations or reimplementations in the crosshairs, so I'd really prefer an Oracle loss here.
And let's be honest, that does make some sense. We've all designed APIs that were particularly elegant and that we were proud of as something almost artistically beautiful. Surely APIs as a whole can constitute some kind of intellectual property.
I'm not sure if copyright is the right way to protect APIs, mostly because copyright lasts for an absolute eternity in software engineering timeframes. But I do think that there ought to be some protection against others copying an API (unless you license it e.g. as open-source), although interfacing with an API should always be allowed.
For example, would I be able to create an airplane with the same cockpit layout (same button/lever positionings, etc) as Boeing so that pilots don't have to learn a completely different layout to fly Umvi brand planes?
The whole programming landscape would need to be audited.
You just them as free beer, because a couple of developers have decided to put their money for you, specially the ISO ones.