Thank you for your reply, and apologies for the delay in the response.
The question at hand is not my aversion to having my code be used in proprietary software; while it does exist, it's not an overpowering concern. I mostly work on Guile these days, which is an LGPL project, so it can form part of a proprietary application. I contribute code under other, more permissive licenses occasionally as well, though it's not my preference. I prefer to work towards a world of sharing, and copyleft is one way to do that. The TGPPL is another way; not as good, but it could be warranted, strategically.
No, my real concern is about the way in which the different contributions come together. Are we on equal footing or aren't we? If we are, then let's all work together, cooperating via the permissions we grant in the licenses, but with no need to assign to some other party. What having a contributor agreement says to me is that "in this project, some contributors are more equal than others." Obviously a properly-governed foundation as the holder mitigates this to a degree, but I don't even think that the FSF assignment policy is necessary for any purpose, and is clearly detrimental to getting casual contributors.