Traveling is not the same thing as driving. You have the right to travel as a passenger in someone else's vehicle, whether private or commercial. You can also walk, ride a horse, etc. You do not need a licence to do any of these things.
But driving puts others at risk, and the government's general authority over public safety allows it to require licenses which certify that the holder knows how to operate her vehicle safely. You have no more right to drive a car without a license than to fly a plane without one.