I don't agree that there is "no such thing as society", but I do think we are a long way from perfection. However, to further discuss that would be to take the conversation off on a tangent. It's not a concern of BA's whether or not someone applying would be better for society in their current role. BA is a business, whose primary goal is to make money. It realises that having high calibre individuals on the front lines makes perfect business sense.
It's difficult to see how increasing the inclusiveness of the programme by widening the financial assistance would guarantee a stronger set of candidates. Having more to choose from usually does get better results, but given that the quality of the chosen few is already extremely high, it could easily be argued the differences at the top are so small and subjectively determinable as to not make much of a difference whether there were more to choose from or not. While it's unlikely BA have the absolute optimal level, the FPP does clearly still acquire very strong candidates in its current form, and therefore there appears little motive to radically change it.