Let's look at the facts.
Kenny Rogers pitched eight innings of two-hit ball to bring the Detroit Tigers even with the St. Louis Cardinals in the World Series. In the first inning, there looked to be a foreign substance on the heel of his pitching hand. In all subsequent innings, the "goop" was gone save for a slight discoloration.
First and foremost, the slight discoloration cannot be attributed to helping his pitching and should be thrown out of the equation. If you get any sort of "goop" on your person, it will wear into the skin if not removed quickly, and a discoloration will be there afterwards, whether it be dirt, or pine tar, or ketchup. A stained hand will not be a stickier one.
Secondly, in the eight innings that Rogers pitched, there was only one inning where the Cardinals got more than one runner on base: the first. After that, Rogers walked two more hitters (in different innings) and didn't give up a hit until Molina singled in the eighth. The "goop" did nothing to help Rogers. He pitched just as well (if not better) after it was removed.
Thirdly, though the stories are different, the umpires did nothing to say that there was a problem. If he was inspected and the "goop" was dirt, fine, it's legal. If it wasn't dirt, then it is Tony LaRussa's fault not to stop the game with him on the mound. The cameras caught glimpse after glimpse of the "goop" but did not catch one shot of Rogers actually applying anything to the ball. Where was that shot? If he knew it was on there, he may have used it. He says he didn't notice it, and there is not one shot of him using it in the game. Maybe he's actually telling the truth.
Anyway, since nothing happened, and LaRussa didn't stop the game and Rogers subsequently washed it off (or actually wiped it off--which would be more apt to leave a slight discoloration) his hand and it didn't appear to be there in the subsequent seven innings, all points are moot. If he cheated, he wasn't caught because LaRussa didn't pull the trigger. Thus, he didn't cheat. Because of this, all other arguments are just a bunch of "goop."