And diving is against the rules. If its obvious, it results in a card for the offender. So they are both breaking the rules. Its the same basis. If they are both breaking the rules to try to win, why wouldn't you be in favor of both?
What about fouling with intent to injure? Its against the rules, and technically illegal (can be seen as assault), but if you put in a leg-breaker tackle on their best player, you have a much better chance to win. Again, its all in an effort to win...