Is it cruel to dock a pitbulls tail?

Unless it is for medical reasons or work, yes. My springer has a docked tail due to the fact she is a working dog and having the long plume of her tail would cause her pain, as it would become easily tangled and matted due to her job. I can't see that issue occurring with a pitbull as they are short haired. Many pitties have their tails and ears docked because they are vulnerable to being grabbed and ripped when used in dog fights, so if that's your reasoning behind wanting to dock your animal's tail then I suggest you rehome your animal and consider your life choices. However the fact you're asking this question suggests you care about your pet so I assume that's not the case. In short: for a fair function/medical reason/practicality: no, if done humanely. For aesthetics/cruel function: yes, it's inhumane and wrong.

There should only ever be a medical reason for a dog to lose its tail so If it is purely for cosmetic reasoning then that is barbaric and unnecessary.

Cosmetic tail docking is banned in certain places along with cropping.

yes

Docking tails is only NECESSARY when the tail has been horribly injured OR if you're showing an AKC show dog and it's REQUIRED for the show ring in the US.

So why would you cruelly dock the tail of a backyard breeder MUTT?

Nekkid - "Standard" for a Pit Bull? Seriously? They're not a breed recognized by ANY legitimate registry so there's no Standard PERIOD for these ill bred mutts!

Unnecessary, certainly. Tails actually do things for the dog, and should be left intact.

Not when they are only 2 or 3 days old. Docking the tail of an adult dog is major surgery cause the cartilage has turned to bone. You are looking at a two or three thousand dollar surgery. Somewhat equal to a leg amputation.

Yep

Why would you do that? No standard for APBT calls for them to be docked. They dont do the kind of work that puts then at risk of tail injuries either

no. That's how everyone will know it's not a fighter.

Extremely cruel. They were born with it and no reason to cut it off unless you are evil.