Simple, if some one wants to buy a type of dog then its thier choice, they are no more a stupid than people buying anything else!!!!!
The people that do need sorting out are those who just let thier dog out to wander and have pups from an unknown breed, any one buying a pup like that will take a chance of how it turns out, eg, someones cute little mugral thats calm and good with kids could have a night of love with an agressive big dog, the pups could end up snappy little killers!!
One little point, arn't all dogs crossed intialy to aquire the traites required?