You read the whole story here:
http://mentalfloss.com/article/85007/how-michael-jackson-bought-publishing-rights-beatles-catalogue
Bascially, MJ and Beatle Paul McCartney were friends. Due to legal issues (i think it was his divorce), he loses publishing rights. Over the course of their friendship, Paul actually explains to Michael how he has bought some other artists' publishing to make money. Michael then buys up the company that owns the rights to the Beatles music, making money off his own friend's art. Paul wrote to Mike numerous times but Mike never wrote back, and that was basically the end of their friendship.
So, if it's cool when Mike does it to a friend, it seems even more excusable when 50 does it to an enemy