Allowing people to automatically gain merit, regardless of their posting quality, would completely undermine the purpose of the merit system.
If someone manages to stick around the forums for weeks on end, writing dozens of posts, without receiving even a single merit... than there's usually very good reasons for that.
I did not say anything about automation
I re-read your posts and I think I misunderstood you the first time around. Sorry about that.
So your suggestion is that users should be expected to receive a minimum amount of merits per week, lest they get demoted, did I understood you correctly?
It's an interesting approach, but you'd still have to account for 1) users taking a break from the forums every now and then and 2) high variance in terms of how many merits one receives within a given period. The latter could likely be alleviated by looking at a long enough timeframe (eg. 1 month instead of 1 week), the question of how to handle periodic inactivity is IMO not as easily answered though.