Apparently some people have started deleting themselves from talks when they receive bad feedback, probably to avoid not being selected for other conferences. This defeats the whole purpose of Joind.In if they consistently do this (which some are doing).
Others seem to delete themselves even before the conference, quite possibly for the same reason, with the goal of adding (or asking) themselves when they get good feedback.
I would suggest making it impossible to add or delete speaker(s) if the start date of the talk has been reached.
I'd be happy to implement this, but would like to receive feedback on this proposal first.