So why can't a slugger like Sheffield or a great leadoff guy like Henderson or a premier reliever like Rocker get any love despite their talent? If we look at recent history these guys have hurt themselves in the past both with their mouths and their actions.
In Rocker's case, even though the Braves tried to trade him last year, they knew they didn't have anyone else in their bullpen who had the ability to get 25-35 saves and worked cheap. The Braves chose talent over character and won their division. They didn't advance past the first round but that can hardly be attributed to Rocker.
Rickey Henderson and Bonilla were teammates with the New York Mets in 1999 and during the final game of the NLCS they were in the clubhouse playing cards instead of being on the bench with their teammates. Bonilla's contract was redone and he was then released and picked up by "America's Team". Henderson started off the 2000 season with the Mets in typical Unhappy Rickey style. He loafed after fly balls; he ran doubles into singles and pretty much pouted until the Mets finally threw up their hands and released him. The Mariners picked him up and Henderson turned into Happy Rickey where he didn't loaf, was adequate on defense and was an important cog on a team that went to the ALCS and gave the Yankees a scare before losing. However Rickey is looking for work right now. Teams - and fans - know his talent but they also know he's pretty old - baseball-wise - not the greatest defender out there and - most importantly - they don't know whether Happy Rickey or Unhappy Rickey will show up.
Sheffield is a different case. There is no questioning the guy's talent as a baseball player especially on the offensive side. But he signed a long-term deal when he was with Florida and now that others have passed him up on the salary scale, he wants to re-work his deal. He has now taken to criticizing his teammates in print and basically blackmailing the Dodgers to either re-work his deal or he'll say terrible things about them in order to facilitate a trade from L.A. to N.Y. or Atlanta. But Gary has left baggage just about everywhere he's gone. He started out with the Brewers and he admitted publicly that he was dogging it in order to be traded from Milwaukee. It's not necessarily the fact that he wants to re-work his deal that bothers fans about Sheffield; it's the baggage he's left behind that is the big problem. Sure, they love his numbers but this isn't roto-ball. They seem to feel that if Sheffield isn't happy on their team, what's to stop him from pulling the same stunts he's pulled everywhere else in order to be traded.
No one is saying that these players are great guys and would be welcome in any clubhouse. But there is a school of thought that goes back as far as the game itself that character doesn't matter as long as you have guys with talent. One of the game's winningest managers was John McGraw. He didn't care what the color of your skin was or what you did off the field. As long as you followed orders on the field was all that mattered to him. There was a time he tried to pass an African-American player off as a Native American but his plan was foiled before the player reached the majors. Not even McGraw's biggest admirers would say he was a pioneer in the field of race relations. All he cared about was winning. If that meant having a guy like Hal Chase - who was suspected of throwing games but was a superb 1st baseman - on his team, so be it.
The great Chicago White Sox teams from 1915 to 1920 never got along very well with each other which was part of the reason key players threw games in the 1919 World Series and went down in infamy as the Black Sox. Many of us recall the Oakland Athletics of the early 1970's. The Swinging A's they were called. They swung their bats well enough to win 3 consecutive World Series but they also swung their fists at each other. Their clubhouse brawls were legendary but they still managed to be the greatest team of that era. The New York Yankee teams of the late 70's had problems getting along with each other and with the manager and owner but still managed to win a couple of World Series. More recently the New York Mets of the mid 1980s won a World Series and a few division championships with a team that didn't get along too well with each other. One spring training Keith Hernandez and Darryl Strawberry fought with each other. Several of the guys on the team - including the manager - were either boozers or coke fiends.
We've heard stories about Barry Bonds being a jerk and several of his teams have reached post-season play. Sheffield has played on a world champion with the Marlins; Jim Edmonds was considered a cancer in the Anaheim Angels' clubhouse before he was traded to St. Louis and he put up MVP numbers in 2000. An article I read last year mentioned a prominent American League player who was rumored to have been traded from two separate teams for having sex with his teammates' wives who has played on his share of winning teams.
So let's not get holier than thou here. Fans can talk all they want about how they'd never root for Sheffield or Bonds or Rocker or Henderson if they were on their team but, if truth be told, we root for whoever is in our team's uniform. A perfect example is Keith Hernandez. When he was in St. Louis, Cardinal fans adored him and the few Mets' fans that came to the park in their down time of the late 70's early 80's hated him. When he was traded to the Mets and the Mets started to win the Cardinals were their biggest rival and the St. Louis fans turned on Hernandez like Hitler turned on Russia. The Mets fans adored him and even welcomed him back with a standing ovation after a day spent testifying that he used drugs. John Rocker has said some things that would make Eminem blush but whenever he runs out to the mound in Atlanta, they cheer him. If he were traded though and he showed up to pitch in Atlanta, he would be booed like he is everywhere else.
My guess is that if a Sheffield or a Rocker or a Henderson were to be traded/signed with/by their team, all would be forgiven after the first homer/save/stolen base. And if that team just happened to win it all, that team's fans wouldn't give a damn about who was on the team, all they would care about is that they won it all. They might even go so far as to say they won it all despite the bad chemistry.