There are breeders and sellers of very dangerous dogs out there.
They are not regulated, nor do they have any scruples that I can detect.
This is taken from a Fila Brasilerio breeders website verbatim:
http://www.sidyboysfoolin.com/FilaBrasileiro.html
"Males of the species can vary in size from 150 to over 200 pounds.
It's impressive size, protective nature and in your face attitude, make the Fila Brasilerio a formidable man stopper, as a property guardian, personal protection dog and gentle family companion. This dog is "made to be beaten".

There are other breeds I personally consider dangerous such as the Presa Canario.
This is from a breeder's website as well. http://www.sanderskennels.com/presacanarios.html
4 years old, 121 lbs. and is very protective...stands 25" at the withers.

These dogs are potentially incredibly dangerous if owned by the wrong people.
Unfortunately these seem to be the people owning these dogs and bringing them into our communities.
There are already too many pitbulls and rottweilers to rescue and many are dying after heartbreaking stints in holding facilities like pounds and SPCAs for no reason other than no one wants them even though their temperment is sound and they would make a good family pet.
If we cannot find homes for these pitbulls and rottweillers, who is going to rescue the Presa Canarios, the Fila Brasilerios, the Japanese Tosas, and the Dogo Argentinos?