Back in 1988, Wayne Gretzky who was by far and away the greatest hockey player in the game and who had just led Edmonton to its 4th Stanley Cup and who was in the prime of his career was traded to the L.A. Kings. He was traded because the owner was having financial difficulties in his other business ventures and along with players and picks that were swapped the Pocklington (Edmonton's owner) also received $15M in cash. Gretzky did not want to leave Edmonton. However, the owner was intent on trading him.
On his first appearance in Edmonton after the trade—a game that was nationally televised in Canada—he received a four-minute standing ovation. The arena was sold out, and the attendance of 17,503 was the Oilers' biggest crowd ever to that date. Large cheers erupted for his first shift, his first touch of the puck, and his two assists. After the game, Gretzky took the opportunity to confirm his patriotism: "I'm still proud to be a Canadian. I didn't desert my country. I moved because I was traded and that's where my job is. But I'm Canadian to the core. I hope Canadians understand that." He wasn't booed because the Oiler fans "cared." He wasn't booed because it is human nature to show no appreciation for teams/players that pose a threat. He was loudly applauded and appreciated because they recognized that he wanted to be an Oiler but his owner/organization kicked him out. He didn't hold the organization hostage or flutter in the wind whether he wanted to stay or go.
According to JSR and Deepie, the fans should have booed Gretzky because they cared or that it's human nature to boo someone that is a threat to their team. It's Again, Gretzky was overwhelmingly applauded. He wanted to stay an Oiler. It was not his choice to leave and the fans recognized that and applauded him as they should have. It was not disingenuine. It was not unofficially orchestrated. It is what fans do. Again, the difference with the Favre situation should be very clear. The GB fans harbor a lot of resentment and bitterness as their hero deserted them. He was not pushed out.
The same will be true when LeBron returns to Cleveland this year. Cleveland fans feel that he deserted them and is a traitor. Cleveland wasn't looking to trade him. They would have given him max amount of money. They tried to build a winner around him (bringing in Shaq, trading for Antawn Jamison at the trading deadline). Cleveland had the best record in the NBA last year so it wasn't like the organization wasn't trying to help him. However, he chose to take less money and go elsewhere and then chose to hold a spectacle when he announced his "decision." Immediately, Cleveland fans were seen burning his jerseys. They pulled down his "We are all witnesses" monument from downtown. Fans were bitter and angry.
Again, it is clear why fans react the way they do. If Favre was truly loved in GB, they wouldn't treat him the way that they do. They would not have booed him after Minnesota's Sunday Night loss where he was battered, injured, and disappointed. If they truly didn't have any hard feelings, they would have cheered him. So the point that they boo because they care or that it is human nature to show no appreciation for teams/players that pose a threat doesn't make sense.