So I was thinking, if you really want to have less shitposters why not change the ranking requirments, make it even harded to level up so shitposters stay away.
Make it something like this:

Rank   Required activity   Required merit
Brand new    0   0
Newbie      1   0
Jr Member    80   10
Member      120   50
Full Member   200   150
Sr. Member   300   300
Hero Member   600   600
Legendary      1000   1000
Copper Memb.   30      1