If one believes that a proposed-but-currently-illegal behavior is beneficial to society, the technically correct way to go about rectifying the situation is to discuss with your local democratic representatives, who can take the issue back to the legislative chamber and work to correct the law. Admittedly, that's pretty impractical at this point.
The taxi driver is just trying to reduce his costs; he could allow riders to negotiate cheaper prices, benefiting everyone.
Given credit card companies have legal means to pay less percentage tax on much more income than the cab driver and suck money out of taxpayers' pockets in many other ways, I'd offer that screwing over the credit card company might benefit the rest of taxpayers more than the cabbie paying tax does.
Fight the power! Stick it to the man!