I'm afraid you are wrong. I implore you to read section 5 of the GPL text. Particularly:
> You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source code under the terms of section 4, provided that you also meet all of these conditions:
> c) You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy. This License will therefore apply, along with any applicable section 7 additional terms, to the whole of the work, and all its parts, regardless of how they are packaged. This License gives no permission to license the work in any other way, but it does not invalidate such permission if you have separately received it.
> If a library is released under the GPL (not the LGPL),
> does that mean that any software which uses it has to
> be under the GPL or a GPL-compatible license?
>
> Yes, because the software as it is actually run
> includes the library.
For this argument, the relevant part is "or a GPL-compatible license". The BSD license is GPL-compatible, therefore I can license my work under the BSD license, and not under the GPL.
For section 5, consider the implications of your quote, especially the final sentence:
> This License [...] does not invalidate such permission
> if you have separately received it.
Section 5 means that anyone who obtains a copy of the work is automatically entitled to a license under the terms of the GPL. It does not prevent additional licenses from being offered, and does not replace additional licenses present on a combined work.
This isn't wholly true - the compatibility is only one way, which was back to my original point. "Compatibility" with the GPL is, according to the FAQ:
> In order to combine two programs (or substantial parts of them) into a larger work, you need to have permission to use both programs in this way. If the two programs' licenses permit this, they are compatible. If there is no way to satisfy both licenses at once, they are incompatible.
A BSD work which depends on a GPL work therefore, cannot be "Compatible" with the GPL because it fails to meet the criteria previously quoted: "You must license the entire work, as a whole, under this License ...".
What you are trying to claim is that you can write BSD code which is API compatible with readline, but if you are not distributing readline with it, it is not a dependent work. (ie, there are other works which are API compatible with readline). The condition here is that APIs cannot be copyrighted. In that case, you can distribute only your code which uses the API under your license of choice, but you cannot distribute the work as a whole under anything but the GPL.
The only point that matters about Readline is that if you link your BSD program to it, then when you distribute the binary, you also have to provide the source to your entire program. This makes it effectively GPL, because the BSD license has no such requirement. That is what the term "viral" refers to.
That's not the case: you cannot distribute the linked binary under any license other than GPL. You can only distribute the BSD code (or compiled, unlinked object code) which calls readline functions, only if you do not distribute readline with it.
If your code makes calls to readline functions, and you distribute readline with it, it is undoubtedly a "covered work" as described by the GPL, and is subject to section 5.c of the license which states that the whole work must be GPL if distributed
5.c says "This License gives no permission to license the work in any other way, but it does not invalidate such permission if you have separately received it."
So you can distribute a BSD project with readline, and recipients are free to choose the BSD license for the BSD part and then distribute a closed source binary linked against a compatible readline replacement. The GPL does not invalidate the permissions granted by the BSD license.
The only goal of the FSF here is that the source code for anything distributed linked with readline be made available under the GPL. They don't stipulate that it only be made available under the GPL and not any other license.
> You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source code under the terms of section 4, provided that you also meet all of these conditions:
> c) You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy. This License will therefore apply, along with any applicable section 7 additional terms, to the whole of the work, and all its parts, regardless of how they are packaged. This License gives no permission to license the work in any other way, but it does not invalidate such permission if you have separately received it.
Also, read this in the FAQ: https://www.gnu.org/licenses/gpl-faq.html#IfLibraryIsGPL