Everyone is entitled to have their opinion, but I strongly disagree that Campbell is a worldclass defender. Firstly, the pros on Campbell is that he is excellent defender physically, and imposing on the air. It is very difficult to outmuscle him, which makes job very hard for striker especially in holding key positions. Furthermore, I think he is very likable guy, who can mesh with team-mates, and defense is all about group effort.
However, his negatives are that he doesnt have the smartest of brain, and any clever forward who have know-how in off-the ball movement, and technical ability can tear him apart. Beside, his ability to tackle is nowhere near the level of Cannavaros, Nestas, Samuels, Chivus, et al. These are players who have far-better understanding and capabilties than Campbell ever had or ever will IMO.
To conclude, Campbell is a very good defender, especially given specific role to perform, but world-class refers to very selective group of players, the very best in the world, the critiera which he does not qualify. Beside, Iluliano, Salas, Tudor have been terrific players in the past, far better than Campbell IMO. It's just that they havent got the legs anymore due to series of injuries and age. As for Olivera, Fresi, Birindelli, et al, they are called role players: Cheap alternative who either have potential and specialist atrributes. Campbell would be quite an expensive role player IMO.