Because it's a trial. If there is compliance and interest -- we would certainly open that number up at a later date.
Not everyone is gonna be interested in EVERY topic they are invited to and we want to cut down on the alerts that people receive..
Are these threads going to be moderated and if so why?
Because the object is to promote more moderate cooperative discussion. And to allow people to explore serious topics with folks they trust and choose without the ever-present interference of trolls and opposing zealots. If you want private discussions -- you can't beat PMs. If you LIKE the constant warfare, trolling and personal sniping in EVERY other USMB thread -- you probably wouldn't use it.
There's no reason why all these threads need to be echo chambers with like-minded people. Although they can be. One hope is that folks will find trusted members "of the other side" to bring in to balance discussions
My personal opinion is that
these Invite Only would require VERY LITTLE if ANY moderation by USMB staff. Other than intruders who simply don't read OPs or don't know what Forum they are in.
Why not make these Invite Only Threads invisible to those who are not Invited, that way not only do you not have to be bothered with getting involved to delete posts and thread ban those who are not Invited but insist on posting, also there would be no problem with the using of the ratings buttons as you cannot rate what you cannot see, you cannot rate or read what you do not know even exists. So the Invite Only Threads would only be visible to those Invited and also to all the Mods but nobody else.
As it is from your OP description etc IMHO these Invite Only Threads as stated are not going to work, if your intention is to restrict in your terms Mega trolls and Ultra partisan Battle Bots it will not work because the former will all still Funny EVERY POST and the latter probably will not want to be involved as it could all be too restricted in general for a full on Battle Bot situation. So based on this I vote No, if the threads were Invisible I would probably vote Yes for the reasons I explain in my paragraph one.