I will do that if you like but I don't agree with your reasoning. One
of the strengths of Unix is that it presents a unified namespace which
covers a number of different data sources. All objcopy wants is a
sequence of bytes, and that can come from anywhere. I don't see why
anybody would ever want to use --add-section with /dev/stdin or with a
named pipe, but I also don't see why objcopy should reject that.
Working with different file types is a feature, not a bug. Rejecting
file types which can work is a bug, not a feature. We can protect the
user from things that are clearly wrong, but we should not protect the
user from doing something that is not clearly wrong merely because we
don't have the imagination to see that it could potentially be right.