Tom Cruise? Easy. When he openly criticized people who use anti-depressants, I would wager that he sparked a controversy w/ at least half of the country - who probably utilize said medication.
Personally, I could see where he was coming from. I would never touch prescription drugs either, but he was a fool for openly criticizing people who ***** at the least little thing to begin with. That ended his status as a hollywood 'golden boy.' His open religious status doesn't help either.
Mel Gibson's case is a little bit different. I didn't think that his movie 'Passion' was anti-semitic, but a lot of people in the Jewish-American community didn't like the tone. They thought it was bias, and spoke ill of their heritage. Throw in a DUI where he's openly making these type of remarks and it makes for a whirlwind that will sell newspapers. Not to mention: Jewish American's run the majority of hollywood. Maybe he'll learn to keep his slurs at home like most bias people too. Of all people, he should've known that Jesus juice would make you talk.
In all: People like to read about young up and coming stars; then, they like to bring these people back down again with lies, slander, libel, rumors, gossip etc. . . Stars are either rising or falling, unless they're smart like the ones with longevity. Those particular ones stay to themselves and stay the hell out of said limelight.
Examples:
Paul Newman, Michael Caine, Jack Nicholson, Phillip Seymour Hoffman, Morgan Freeman, Johnny Depp, Matt Damon, Christian Bale, etc. . . You get the idea. These people live in obscurity and you really only see them onscreen or when they're doing promotions. That's why they're respected thespians. If you know too much about a person's offscreen life, it ruins their performances imo.