I can see your point of view, though one nitpick: the GPL doesn't prevent shenanigans any more than an MIT license. With a CLA, the owners can relicense the code as a non-open source license. With both MIT or GPL, you retain the rights to develop the previously released code.
It's the FSF's commitment (mentioned upthread) to not do that which arguably makes it safe to sign a CLA with the FSF.
It's the FSF's commitment (mentioned upthread) to not do that which arguably makes it safe to sign a CLA with the FSF.