DJ's points are absolutely right.
If I were a Welsh taxpayer, I would be very concerned at my hard-earned cash going to support a holiday getaway enterprise. That would be like subsidizing tour operators! Yes, a few jobs are maintained through outbound tourism, but allowing our countrymen to spend their cash abroad can't ever be a governmental priority.
The real prize, and the only possible reason for public investment in an airport, is to positively enhance the economy through inbound tourism and foreign inward investment.