1) Let's let the number of street parking spots in a city be equal to 10. Currently your new duplex would keep that number 10, assuming 2 cars per household. Under your plan, that would reduce the number of street parking spots to 8, assuming the same number of cars per household. Of course now that the law has been changed, more people want to build duplexes, to take advantage of thier property. 4 more duplexes are built in the city. Now you have zero street parking spaces remaining. So where do new vehicle owners park? They have to pay. So your new rule has transferred what was previously a public expense to a private expense. Basically upping expenses on vehicles for others is ownership infringement. It would be similar if someone built a factory next to your house which used up 99% of the water in the city and then said..."how am I infringing on water usage? I paid for it." Well, yes but no one else can use water now, or you have upped the cost of water for the neighborhood.

2) People often use cars to generate income through being able to drive to work.