O'Reilly isn't a Republican. He's specifically quiet about his political leaning and agrees and disagrees evenly with both sides. Actually, he seems more liberal than conservative - my husband doesn't like him for this fact, actually (my husband's a Beck Lover) . . . but he does feel it's ok to torture.
He's also not the typical "Fox News" voice. He's set apart from them and just happens to be on their channel. He'd fit in just fine somewhere else because he doesn't need a V8. He says what's on his mind and that's that.