I rather think the planning for the extermination of mankind was done mostly by the Cavils, with support from the others. The twos are convinced enough of their holy mission to do anything, the threes have a mean streak, the fours have no qualms in experimenting on helpless humans, the fives were pretty vicious with Baltar, the sixes have no problem killing babies or beating Tigh senseless, and the eights are just naive enough to go along with everyone else in the hope that things will turn out all right.
I have no problem believing the seven decided to exterminate humanity with no outside programming or brain washing.

__________________
"You miss 100% of the shots you don't take" - Wayne Gretzky