Promoting members gives them significant responsibilities. If they aren’t prepared for the role or don’t take it seriously, it could have adverse effects on your Tribe. Screen your members carefully and promote only those you know and trust.
For example, Co-Leaders can promote anyone as Co-Leader, and can kick almost anybody in the Tribe. Elders can accept new members. This leaves a lot of room for dirty politics if handled improperly.
Kicking people for no reason might be a mean thing to do, but it’s not against the rules. So, preventing it is up to you!
We can’t retroactively change Trive dynamics in the event of one bad apple. We like each Tribe to be pretty much independent.