I know what the GPL does, but there are people who are scared away from it
due to the forced copyleft nature. There have been reports about corporations
more willing to contribute back to code under the Apache 2.0 license than the
GPLv3. It is true that from this angle that it allows them to lock up the
code under a proprietary license.
Maybe that's why newer licenses like the Mozilla Public License 2.0 were
released. The code that was MPL 2.0 licensed will stay that way in all of its
copyleft nature, but it can be linked to other licensed code and keep its
copyleft status as part of a "larger work" whether it is proprietary or not.
It also appeased to the FSF crowd being GPL v2+, LGPL v2.1+, and AGPL v3+
compatible where technically GPL linked code would cause a dual licensing
structure between the MPL 2.0 and the GPL.
Back on the client that may use the code: You can explain the GPL and they
will still not be convinced. That is why a dual-licensing structure may be
possible so they won't "freak out" when you give them the code. The core
source code will always be GPL'd until the end of time. Its just that some
users have to be prepared to dual license for the client sometimes.
