I might be teaching you to suck eggs, but I suggest that the best way to implement this is to have just one list and an 'include/exclude' flag that applies to every person listed.
Initially it seems like this is the best approach, but then you have to ask how do you handle those not on the list. Attempting to answer this question leads to the conclusion that unless the list consists of all members (too unwieldy) that it must be a member subset that is either inclusive or exclusive.
This also leads to the conclusion that the member group concept is required. For example, creationists could be one group, evolutionists another. In this way you could control thread access by placing members and groups in the list. Threads just for evolutionists or just for creationists could be easily created. Members could join many groups, but there would be the need for classifying groups as mutually exclusive. For example, one wouldn't want someone to be able to be in both the creationist and evolutionist groups, or in the theist and atheist groups.