We believe that most of the people in the world are basically honest. We've driven all over the country with boats on the car and people haven't given them much notice other than "cool boats!" Of course, we don't park the truck on the south side of Chicago with five-grand worth of sea kayaks on the top and leave them for the weekend.
The good news is that Thule has a great set of tools to keep your gear from all but the most persistent (often professional) thieves. The better news is that professionals take the easy stuff first, so park next to someone without locks.