The thing that the FSF makes contributors sign isn't a CLA; it's a copyright assignment agreement. It goes much further than what's described in this article; rather than merely shifting the legal risk around, it makes it so that the FSF, not you, is the owner of the code that you wrote.
Obviously, something like this carries substantial potential for abuse, and so would generally be treated as sketchy and an indicator of bad faith if done by anyone else in the FOSS community. The FSF gets away with it because they have a long track record and everyone knows there's no way they're going to pivot to a proprietary-software business model.
The reason the FSF requires copyright assignment is because they want to be able to proactively sue GPL violators (because doing so is a way of furthering their core mission), and U.S. copyright law makes it difficult for anyone other than the copyright holder to do that. Most other organizations' priorities are such that this would be a waste of time for them.
> U.S. copyright law makes it difficult for anyone other than the copyright holder to do that.
Or, rather, the FSF originally believed this to be true. This HN post from today[0] is an instance of someone other than the copyright holder suing for GPL compliance. They are not claiming any kind of copyright ownership over the GPL code that they're suing over. We know now in hindsight that the FSF was overly cautious about this.
An interesting tidbit is that the GCC project (under the FSF banner) recently stopped requiring copyright assignment to the FSF[1]. Mostly because they want to distance themselves from the FSF, but partially because it didn't turn out to matter after all. A developer certificate of origin (DCO) suffices for their purposes.
While true, the old approach (having a single contributor / partial owner, not necessarily an FSF-style copyright owner who owns the entire work) still doesn't require FSF copyright assignment. As an example, the Linux kernel never did copyright assignment, and the SFC has been suing over GPL violations for Linux.
Obviously, something like this carries substantial potential for abuse, and so would generally be treated as sketchy and an indicator of bad faith if done by anyone else in the FOSS community. The FSF gets away with it because they have a long track record and everyone knows there's no way they're going to pivot to a proprietary-software business model.
The reason the FSF requires copyright assignment is because they want to be able to proactively sue GPL violators (because doing so is a way of furthering their core mission), and U.S. copyright law makes it difficult for anyone other than the copyright holder to do that. Most other organizations' priorities are such that this would be a waste of time for them.