Because they are used as fighting dogs and have a bad reputation for attacking people for no reason.

because in media you never see anything positive about them, only negative news pic for you ... :)

Because, personally, I find them dead ugly. The last dog I would want to have.

People fear what they do not understand.

No doubt about it, they are powerful dogs. Bred to take down charging BULLS even. Their fighting instinct is strong, and when they start, they don't stop until the fight is over or their Master tells them to. They only have ONE Master their whole life. But, they are wonderfully loyal dogs, and will protect their home and their people to the last breath. It is sad that the dog-fighting business is so strong to this day... you'd think we'd come further as a society. Until this HORRIBLE practice abates, I'm afraid our best friends will be looked on as the black sheep of their species.

A few rotten people, ruin it for the many. A lack of education, poor breeding practices, poor training practices can create more aggressive dogs. This can happen with ANY BREED OF DOG. The "Rule of Thumb" is that ALL DOGS BITE! It is simply a matter of WHAT will cause a particular dog to do so. Because of the unique design and jaw strength of a Pit Bull, if one of them does bite...it is generally much worse than most other dog breeds or types out there. Then too ALL terriers, of which the Pit Bull has a lot of that type in the blood lines...during development... have a VERY strong Prey drive. Terriers were developed originally to be "varmint dogs," to go to ground, to be strong willed especially about going after a critter. This sets up the PB to be geared to enjoy going after other animals. Now....over the past 12 years or so, there have been PB breeders who love the breed fully and have bred them with the goal in mind to create puppies with LESS of a prey drive, and more tolerance for other animals. As a rule, PB's are NOT human aggressive. That is not normally the problem, it is the prey drive against other animals that is the main issue. Unfortunately, this often hyper drive can translate to going after small, quick-moving children, or even adults who appear to be "jittery" or stressed around such a dog. But, as said, NORMALLY Pit Bulls are wonderful with most people, loving, loyal, playful and responsible animals...the few and the design of the bite, coupled with pretty rotten humanbeings cause the REAL problems.