You do have to file something ~ tell the party you are going to run. In Virginia the Democrats go out and get the nominating petitions signed.
Look, a political party is a coalition ~ it has factions. In too many cases we have petty little POS who feel advancing the interests of their faction is the most important objective.
Primaries should help the voters revise thinking. As it is in Virginia our top dogs in the Republican party are rapidly destroying their own careers by cheating on behalf of Romney.