Here's another suggestion, all airdropped merit stays but smerits declays. Now when a user, get certain amount of good report against them for spamming, they get punished by removing some airdropped merit. Could be 15 merits per every 5 good report against them. This way, only the spammers get affected. The report used for this punishment has to be strictly spam related.
Your suggestion is demerit, right?
But I think demerit 15 points for each 5 good reports (mean 5 bad posts) is very very strict. It should be reversed as 5 merits per 15 bad posts that reported by forum users, and handled with agreements from staffs. With the reversion of suggested demerit, I still think it is strictly.
It will cause massive complaints, so in my opinion it is good if the period of permanent bans expand longer, because it will not demerit, derank, just put bad posters in longer temp-banned jails.