I see your point and the problem you are addressing is real. However how to ensure that the "terminator" would act according to the spirit you've outlined and not to his own personal biases?
Being a terminator/merit patroller (I'll use terminators in my post) is a privilege, and can be taken away from you at any given time.
As there is likely a low amount of terminations (few people able to do it, with limits per person), there should be a collective page publicly showing all terminations (as part of the merit stats).
In first instance, terminators would regulate and check themselves. If a terminator goes out of line, the others report it to theymos and the position is taken away from them/their actions are being undone.
I have to point out that this very OP is calling for a way to delete the merit that the OP of DeepOnion is receiving by its community.
This is not exactly the case you have been advocating. You may like or not like DeepOnion, but that is not a case of accounts farming and the OP of their thread is not exactly irrelevant since it has got so much follow up.
My reply is indeed only indirectly related the OP.
I took this thread to suggest the system as it is one of the threads currently discussing options to reverse merit or introduce negative merits.
It simply was the first thread when I opened Meta that discusses this, so I decided to post in here (instead of opening yet another thread about the same topic).
Which remind us of the old Latin quote: Quis custodiet ipsos custodes? = Who controls the controllers?
Theymos.
One question though - do you suggest this happen only with already Merited posts? i.e. if a 'Terminator' (sounds fun terminology!) sees a spammy/extremely low quality and irrelevant post, and it isn't Merited, can they still 'DeMerit' that post, so the total Merit of the account goes down? Or is this just for already Merited posts only?
No, this would only apply to merited posts. You could terminate a post without merit and thus keep it from getting any merit in the future (as long as you have the terminator privilege),
But keep in mind that the terminations you have are limited, so it would likely be a waste of a termination.
You could not remove merit from someone by terminating one of their posts that isn't merited in the first place.
Reading up on this, I like the idea.
I called the usergroup "merit patrollers" because of something like this. The Patrol page lets you browse posts from Newbies and is meant to ease up reporting/moderation.
A Merit Patrol page could be formed that shows merited pages and eases up merit-"moderation".