if you know the other teams plays, know when they run them, its an order of magnitude easier to stop them or take advantage of them. end of story. talent matters yes, but knowing another teams plays ahead of time so you can easily counter them and give your players a huge advantage is not in the spirit of any game. in the very least, its extremely unsportsmanlike, and it cheapens what happens on the field by the players. when you cheapen what occurs on the field, it cheapens the game as a whole, and people will stop taking it seriously as fans.
for example. if, hypothetically, there was a QB who plays amazing in college, everybody wants him, gets to the NFL and suddenly cant do anything close to what he did in college when it comes to reading the field. people dig and find out his college coaches knew the opposing defenses plays, allowing that QB to know exactly where and when to throw with relative ease and safety, thats a player who is a FRAUD!!!!. Fraud player goes on to cost others their jobs, money, reputation, etc because he isnt what they thought he was.
we assume as fans that every game is a somewhat level playing field rules wise. you take that away and you become "professional" wrestling.
if yer not cheating, yer not trying hard enough, is not a valid excuse at the amateur level, and frankly, the pro level as well.
how some cant seem to grasp this boggles the mind.