All the good guy factions fight them all the time. I've fought the Sith in PVP for a year now, and Imps in PVE for two, going on three. I've done cult slaughter since the CIS's early days.
Why do these have to be the three big PVE enemies for most of the Paragon factions? Can we fight droids bent on the domination of organics? Maybe some kind of parasitic beasties? Some kind of big menace that requires the Sithies to work with us to achieve victory?
STOP MAKING THREADS ABOUT KILLING THOUSANDS OF STORMTROOPERS. IT IS KILLING THE EMPTY HALLS WERE MY SOUL WOULD BE WERE I NOT HALF-GINGER. BE INTERESTING IN YOUR DOMINIONS AND FACTION THREADS.