Well, if ethics was that important, Ty Cobb wouldn't be in the hall. He was a bigoted, disrespectful human being in general. He jumped into stands once and beat up a handicapped person, stabbed a black hotel worker, and yelled racial epithets to any player of recent immigrant background (German, Italian, etc). He was the "gangsta" athlete of his era. In today's game, Cobb would be beaned almost every game to the point he'd couldn't play anymore. Baseball is known to police itself on the field, makes me wonder why Cobb wasn't taught a lesson by opposing players too often.
But today's standards are different. The game of baseball is so intertwined with the identity and culture of the United States, that each inductee is now judged on how they represent themselves as human beings, not just a player between the lines. To give a player a pass into the Hall in spite of his poor character, would be a bad reflection on the country's ideals.
With that said, Pete Rose's gambling directly damaged the integrity of sport. We never know if he gambled on games while as a player. That doubt is why Rose will probably never get inducted.
The steroid issue is a little more in the gray area. Steroids don't directly "fix" the outcome of the sport, at least not in the same way as tanking a game, scuffing the ball, or sanding down the side of a bat. Nor were they against the rules until recently. When pitchers were gumming up the ball with spit back in the day, they weren't called "cheaters." It wasn't against the rules at the time. Why should roid users be held to a different standard?
There is no direct evidence that McGwire, Sosa, or Bonds did roids. But Palmeiro was caught during a time when it was against the rules, therefore his eligibility is in serious jeopardy. But I think all others should get a fair shot.