I realise this is an old thread that's been necroed but it raises an important point.
I feel, like most people, that Minecraft is best played as a PvE game. Mojang added the option for PvP for a reason though and whilst that playstyle is relatively unpopular dismissing it entirely is arrogant; as has already been said, there is no "illegitimate" way to play a sandbox game, especially Minecraft which is the sandbox to other sandboxes; the most extreme sandbox in gaming. People who define "legit" and "not legit" play styles for their Minecraft are just setting their own personal rules they feel comfortable with and imposing them on other people. It's important not to forget that.
On the actual matter at hand, I don't feel FTB is really designed for PvP play so you're going to struggle to find a server. A PvP version could be fun though, but it would have to be very carefully balanced in the configs.