Agreed.

IMO an individual should be able to select being not interested in a thread therefore making this thread not appear anymore in 'Active threads'. This makes 'Active threads' personal; more useful with information the user is interested in, based on blacklisting.

I don't know if this is possible with vBulletin because it'd require additional information stored in the database (additional fields in user's profile as saved in MySQL), and also this would need to be queried every time a user is logged in and browses around t.m.o. If you want to also extend the function to when browsing (sub)forums, more queries. There also should be an unignore option.

A workaround may instead of using 'Active threads' subscribe to threads which is essentially the same as whitelisting without changing default 'lists'.