I think that cycle sometimes happens, but I think it’s more common for a community not to be ruined by sociopaths, but rather too many mops, whose mere presence taints the community and the brand for everyone else.
It’s rare for a member to convert from a lower tier to a higher tier. In most cases, it’s not worth it to have a way for people to pay you $2, $10, $50, in hopes that they’ll upgrade. If they’re happy with the $2 they’ll stay there. If they’re unhappy, they’re more likely to churn than upgrade.