I'm all for preaching to the converted. It tends to remind people of what they believe in. Look at how right wing radio has galvanized the Republican base.
A short list of powerful and political artworks:
Guernica --Picasso October 1977 --Richter
Third of May --Goya
Philip at Fraga --Velasquez
Charles V on Horseback --Titian (shown left)
F-111 --Rosenquist
Porkopolis --Sue Coe
99 Cent Store --Gursky (shown left)
Raft of the Medusa --Gericault
Target with Plaster Casts --Johns
Mother with Dead Child --Kollwitz ... -- Mark Shetabi is a painter and installation artist