Personally, i don't see why people mod.
if you're in it for JUST winning, and not the justifications behind it, IE vindication of your own talent and wracking yourself against competition and the constant race for points, that's what racing's about. not just winning for winnings sake.
if you're cheating to win, that just takes out the fulfillment of it, the entire point of racing is a clash of skill and sportsmanship. i just don't understand why'd you'd ever want to cheat yourself out of the best part of racing.