There is a "'fee' to pay taxes using cc's" because if there were not a fee, you would have the FFP equivalent of a perpetual motion machine, and there are no perpetual motion machines.

Credit card companies do not fulfill their simple existential purpose, that being to make gobs of money for themselves, by advancing you money and also giving you valuable consideration (airline miles) for the privilege of doing so in return for nothing other than your possible gratitude. While a great many merchants will subsidize that extension of credit and grant of other benies to you by paying the credit card company in the range of 2% to 4% of each card transaction, the IRS sees no reason to accept less than 100% of what they think you owe them. So when the IRS is on the other side of the deal, you must be the one to pay the credit card issuer their "vigorish." Some of us think, though, that this may be one instance in which the "vigorish" makes sense.