The effect as is is enough, you cannot spread the corperation at all, and you loose all benifits from any franchises in you nation, or any other nation with SP
The franchises in nations not running SP still function, why should they stop working just because their parent company is now state owned.
We can continue to debatye if its an incorrect game balance issue, but the fact that it already "mimincs" the real life situation, would religate it to "Not a Bug"
Well SP states do, as my examples show. They would be loath maybe to spread the corperation, but its existance abroad were it takes money from the capitalist pigs, would be seen as a state asset