This is correct. But then probably the whole procedure of joining to a campaign should be changed, from privately giving out addresses (by participants and possibly by campaign manager too) to private access to the spreadsheet for the participants.

However:
* this would be a huge hassle for CMs
* since members come and go the spreadsheet can become sooner or later almost public again if it isn't that everybody can see only his records
* this means that neither the CM nor the participants cannot be properly checked; and humans are inclined to cheat, you know...

So.. this half-solution is imho more hassle for not much of use/improvement, and.. I don't know how can this be done really good.
Don't take me wrong, I'd like to see a better solution. But for now, we don't have one.