I cant think of any reason why any fan of a team outside the top 6 would support financial fair play in its current format.
The rules are designed to protect the position of the already established clubs and restrict the investment an owner can make to try to better a club
The best clubs can keep spending and pushing prices and wages up, without the fear of getting it wrong, because they will spend more on more replacements if necessary. But if other clubs try to do likewise to attempt to remain competitive, they will fall foul of the P & S rules - even if the owner is investing their own money into their own business, with no concern on the sustainability of that club.
If the rules are there to stop football clubs from getting into financial difficulties then they aren't fit for purpose.