Why don't we burn them at the stake too? This type of attitude towards modified cars is a total witch hunt, as are the extreme restrictions placed by CARB.
Essentially, modifications should be measured by their effect. Exhausts should conform to a decibel limit, whether stock or modified. Cars should conform to set pollution standards under all settings.
Too many rules, too many restrictions, too little reason. It's not like they don't have enough real crime to fight.