Vicar in the USA, where Pitbulls aren't banned they are assistance dogs, rescue dogs and police dogs. So, it's not true at all that they serve no purpose other than fighting.
However, Lennox was not a Pitbull or Pitbull cross. He was a labrador/american bulldog cross and described as 'pitbull type' because he fitted the measurements which deem a dog of pitbull type, as do an awful lot of pedigree labs and other dogs too, none of which are pitbulls or theri crosses. His owners adopted him in good faith, as no doubt the Dogs Trust rehomed him in good faith and neither of them were wrong as the dog was not a pitbull cross.
Pitbull types are allowed within the law provided certain conditions are met, they are not completely illegal just for being them.
Do we really want a situation where the authorities can come into our homes and take our much loved family pets, which are owned responsibly and taken on in good will, not pitbulls or their crosses and kill them, just because of how they look.
Aside from which, although we should not allow dangerous dogs, dogs should be judged on their behaviour and temprement, not on their breed or how they look.