I agree that there are legitimate government functions - national defense being at the top. And as long as roads are publicly-owned, not private, obviously they must be paid for by taxes. Public transportation, however, never having paid for itself in any city, is simply a transfer payment from those who don't use it to those who do.
And yes, I realize there are taxpayers who don't use the roads who are also getting the shaft. That number, though, is much smaller than is the case with public transportaion. Even so, it should be mitigated through tolling whenever possible.