There are certain requirements that need to be in place in order for a car to be legally on the road. If we abuse the priviledge of letting us be able to take care of those requirements on our own than sooner or later the state or government will make those decisions for us (California is a perfect example and don't forget all the states the require "safety" inspections). That doesn't come free. Higher taxes and licensing fees will cover the extra expensses the state will have to do these inspections!
We don't get to pick and choose the requirements that we are going to meet. If we are resposible enough to drive than we should be responsible enough to keep our vehicles in good working order and at least meet the minimum requirements that have been set to have the vehicle on the road.
As far as emission are concerned, If they have been altered or tampered with than the vehicle is no longer eligiable for on road use and cannot be sold for on road use. It is one of the minimum requirements that needs to be met for the vehicle to be on the road just like a car doesn't belong on the road with a bald tire(s), exterior lights that don't work, or expired tabs.