It is limited to people who John Locke knows and would be surprised by, so these far-fetched ideas that keep coming up just don't fit well for me.
How long has Michael and Walt been gone? Maybe Michael and Walt experienced a time off the island that was similar to the not-so-great circumstances Jack, Hurley, and Sayid seem to be experiencing once they get home. Also, if Ben can get Sayid to work for him in the future, why not Michael? Maybe Michael wants to get back to the island, and he's going through Ben. Although, the Losties aren't going to be so thrilled having him back, I'd imagine, after his fiasco. So that doesn't fit well. More likely Michael would be driven by force or something.
"We need someone on a freighter."
"That guy will do it. Just take his kid away. He'll do anything. He shot two people to get his son back."
"Oh, okay. Nice."
I'm also of the group that enjoyed Harold's performance as Michael, and think it's a brilliant idea to bring him back this way, even if it ruins the big reveal for all us hardcore fans. Ben kills people, and he's quirky, but I wouldn't want him off the show for those reasons. I like his performance as a villain of sorts. If you didn't like Harold's performance, however, then I see your point. But Michael is cool.