What's behind the antiabortion campaign over "fungibility"?

A US Republican Senator argued that the US must refuse to subsidize foreign family planning (FP) organizations that use their own funds for abortion-related activities because to support them would indirectly support abortion, since "money is fungible." The "Mexico City gag rule" advocated by Republicans would stop US-funded agencies from providing legal abortion or from engaging in a range of legal advocacy activities with their own money. The fungibility or interchangeability of money is the acknowledged price governments pay to have the private sector deliver services in all arenas, yet it is only deemed a problem where abortion is concerned. This argument has also been used by various states to attempt to bar certain FP organizations from receiving state funds, but the courts have struck down such laws. Missouri is continuing to attempt to draft a law that will survive in the courts. The current effort involves relitigating previous attempts to cut off aid to abortion providers and, if that fails, excluding all nonprofit groups from the state FP program. This extreme proposal would require the state to create its own network of FP centers at great cost. No one seems concerned about fungibility when the US is funding international relief agencies tied to various religious denominations or giving foreign aid to countries where abortion is legal. The gag rule also ignores the fact that FP agencies seek to prevent the necessity for abortion by reducing the incidence of unintended pregnancy. This hypocritical "anti-abortion" strategy results from the frustration of abortion opponents who have been unable to outlaw abortion in the US.