I should have specified that the Audacity CLA allowed Muse Group to relicense Audacity from GPLv2 to GPLv3. Yes, I agree with you that not all CLAs are bad. While you keep the copyright to all your contributions, because the copyright is assigned to them (? I'm not actually sure about this), they can relicense it. The CLA agreement.

You grant MUSECY SM LTD, an affiliate of MuseScore and Ultimate Guitar, (“Company”) the ability to use the Contributions in any way. You hereby grant to Company , a perpetual, non-exclusive, worldwide, fully paid-up, royalty free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute your Contribution and such derivative works.

There was quite a lot of confusion and outrage about this at the time, so I can't recall whether Muse Group specifically said they wanted to include Audacity in Apple's app store or this was given as an example of why the CLA could be beneficial. My rebuttal was this is not a particularly noble cause. There was also the argument that the FSF requires you to sign a CLA for its own projects so it can reserve the right to relicense it if it benefits the project. My rebuttal to this was...well, it's the FSF. The day the FSF relicenses their software under a non-free license is the day they die.

All in all, I'm not worried yet.