fixing up your car

i own a 1997 honda civic ex coupe that is orange. in the car i have a AEM intake system, megan racing headers, lambo door kit, an exhaust tip( i plan on buying tanabe or greddy catback), ksport shocks, tyc headlights, bomz racing wing, taillights i purchased off of ebay, new seats, removable steering wheel, tinted windows, lcd radio system, 2 phillip 120 watt speakers in the trunk, 2 tweeters ( plan on getting amps). i find it ridiculous how merchants are able to sell car parts to people and the same time it is illegal. many buyers do not know that for the intake system to be legal it must have serial numbers on it. also headers must have serial numbers on them, there are very few manufacturers that make street legal headers. as you have seen in movies Fast and Furious the neon lights below the car is also illegal. for exhaust systems there is also a sound limit to how loud the exhaust can make. how is it that people are allowed to sell all these after market parts and they are illegal. it is like how drugs are illegal, you do not see grocery stores selling grams of marijuana. if merchants are able to sell car parts freely why should they be illegal?