Here in Israel the election campaign is in full swing with mud slinging and charged advertising campaigns everywhere. The surprising thing is that very little effort is targeted at convincing the voter at the political centrum, because she will decide the election.
Targeting your existing supporters with messages they already have bought in to will get you lots of likes and support, but will make little impact on new potential voters. Think about those voters that sit on the edge, how can you tip the balance in your favour?
The same is true for almost any presentation. Your followers are already on your side. The haters will never agree. You need to target the ones that have not decided yet.