FSA dollars are use it or loose it. Those fortunate enough not to exhaust them are forced to spend or surrender their leftover money at the end of the year. This is not a good use of resources and leads to wasteful consumption or a penalty in earnings likely greater than the tax savings.
Allowing americans to donate extra FSA dollars to organizations eligible to receive tax-deductible charitable contributions would be tax neutral and provide vehicle to more efficiently use leftover funds.