I'd always include a silence. Keeper is always good to kill a deadly minion that hides behind a taunt or for lethal as you said. I wonder most topdecks don't have a silence I guess because the odds of having a silence in hand when needed are so low compared to when you do 100+games to climb to legend.
Anyways I hate to lose a game just cause I can't get past that 8/8 taunt or buffed minion hits me too hard and I can't do anything against it as a druid. Other ideas is to include BigGameHunter
I'm 3-0 with this deck so far, and haven't needed a silence yet. I keep waiting, though, for that paladin opponent that stacks some god awful huge-ass divine shielded taunt in my way that I have no way to deal with.