Does that title really require someone to be FROM the working class? I always thought it was more about who they fought for.

Take Che Guevara, for instance — the guy was from an upper class family who could afford to send him to med school. So was Marx, whose father was lawyer with a comfortable income who could afford to have all of 9 children (though not all of them survived). And John Lennon, who wrote the song that inspired the meme, had already had an enormously successful musical career and was quite likely a multi millionaire by that point.