As an example, the Z80 and the 8080 were interoperable and it was better for everyone.
The Constitution only says
> The Congress shall have Power [...] to promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.
most of copyright is defined in statute (the various copyright acts) and court precedent.
Most stuff in the Constitution gives the government the power to do X (sometimes stating explicitly that it's for reason Y). The structure of the copyright clause is that Congress has the power to do Y, using mechanism X — a strict reading of that means that the government cannot do X for reasons other than Y, and cannot pursue Y using means other than X, and definitely shouldn't do X for reasons of not-Y.
Every programming language has stolen large portions of their API from other languages. Even Java.
Remind me: Did Microsoft file an amicus brief in this case? If so, on which side?