Play the Donimion/Founders when they are released as a faction them, thats more their style. The Federation isn't about mass murder, except Section 31 and that attempted genocide of the changelings.
As a fed member I am about genocide. It's called being fedcentric and all others being the enemy. You're right about Star Trek lore and the Fed being about diplomacy and peace of course. However, I am not and I play fed.