Soooo much bad information in this thread! It isn't "What car shouldn't exist" it is "what car don't you like?"
The Smart, in europe at least, makes a lot of sense. Smaller, easier to maneuver, easier to park, and without all the 19million tons of american safety equipment, better gas mileage. In the US, however, they get terrible gas mileage for what they are. (frankly I hate the things.)
The Hummer makes an EXCELLENT limo, for one reason: it has a strong enough frame to support the stretch. Virtually any other stretched limo is likely to bend due to insufficient structural strength.
The majority of all large SUVs have no real purpose other than Road-arms-race, and ego of the owners.