Terrible analogy. The number of people that would even have any desire to put something illegal in taxi luggage is very low. The number of people wanting to launder money because they did something truly evil is very high.
International airlines are a better analogy; should we just let people run weapons, drugs, even children in their luggage, with no mechanism for inspection?
It's not necessarily disposing of a body, and punishing people for moving luggage around without asking questions is obviously absurd.