Back before SE implemented activity logs for the FC chest our FC had all of it's gil stolen by a member. It wasn't an RMT - just a selfish thief. However SE's take on it was "you gave them access to the chest, and gave him the right to access the gil. You shouldn't have trusted him."
So I know first hand how this type of thing sucks.
I agree that you shouldn't be able to promote above your own rank - that would be the same as allowing someone to promote themselves.. (though if you can promote above your own rank, you probably CAN promote yourself.. I should try that.. )
However I don't think it's unreasonable to restrict promotion to a very small trustworthy group of people. It's not like you have to go changing peoples ranks on a daily basis. (I should also qualify that our FC is relatively small (<100) and for the most part we all know each other pretty well. So in fairness, if you have a very large FC, it might be different. )