Note, this case did NOT say the law was bad, but that it is an attempt to impose a STATE REGULATION where the Federal Government has said it was EXCLUSIVE REGULATORY Rights,
This is the same rationale people are using to undo the immigration restrictions imposed by various states, That immigration is a FEDERAL AREA OF CONCERN and thus the States can NOT entered that area UNLESS the Federal Governments permits them.
In this case the Federal Congress gave EXCLUSIVE control over meat handling to the USDA( United States Department of Agriculture) and it is clear that Congress did NOT give the State any rights in this area of the law. Since federal law forbids the use of Road Kills your comment is irrelevant, for the use of Road Kills are already illegal by FEDERAL LAW.
This can be seen in the opinion:
In 2008, the Humane Society of the United States released an undercover video showing workers at a slaughterhouse in California dragging, kicking, and electroshocking sick and disabled cows in an effort to move them. The video led the Federal Government to institute the largest beef recall in U. S. history in order to prevent consumption of meat from diseased animals.
In conclusion of the opinion Justice Kagan writes:
The FMIA regulates slaughterhouses handling and treatment of nonambulatory pigs from the moment of their delivery through the end of the meat production process. Californias §599f endeavors to regulate the same thing, at the same time, in the same placeexcept by imposing different requirements. The FMIA expressly preempts such a state law. Accordingly, we reverse the judgment of the Ninth Circuit, and remand this case for further proceedings consistent with this opinion