Virtually none of the emissions components on a modern vehicle are detrimental to its performance because the vehicles are designed to work with them from the start, so there's very little improvement to be gained by removing or disabling them. If one of the components has a problem then it should be repaired, just like maintaining anything else on the vehicle. The emissions laws don't require vehicles to pass anything more stringent than what they were designed to pass originally, so if a vehicle doesn't pass then it just needs maintenance or repairs to bring it back to it's original working order. Maintenance and repairs are just part of the responsibility of owning a vehicle.