Unfortunately this is something the GMs can have no control over. If a FC forces you to donate gil to get a house, LEAVE. Such is the way of MMOs where leaders have most of the power and its up to the followers to determine if the leader is going to be a good one or an a-hole. Unfortunately there is really no way for GMs to police this issue because scenario A is what you are describing, scenario B: guy spends 5 mil on house, leaves FC, puts ticket in to get reimbursed (some money to all i think is what you are refering to.) then proceeds to join back once he gets his money back.
There is just too much abuse that could come from it. Personaly we asked all of our newer members not to contribute if they did not want to. and only if they were absolutely aware that they would not be getting any money back.