If we want to say "In Spain, paella is eaten" , then "se come" would be the obvious answer. When the sentence is "In Spain, people eat paella" there is a nominative word here. People. There is another translation for the third person plural in this case, no? Or would you have to explicitly say "En España las personas comen paella?" I'm sure I have seen uses of "se comen" without an explicitly named plural subject...