Boosting compromises the integrity of the game. It affects all stats and rewards. It's like steroids in baseball in the 90s-00's. It skewed that era's stats and rewards (e.g., pennants) beyond any degree of reliability.
You can say who cares if Barry Bonds is not on the opposing team today; just move on, he'll not affect whether you win or lose this game. But that would be absurd, wouldn't it?
Cheating is cheating, and it ought never be condoned by one's inaction. If a kid today cheats in a meaningless video game, chances are that same kid tomorrow will cheat in other aspects of life. Aspects that affects others in real life ways. Wall Street boosters (speculators) come to mind.