Politics almost always detracts from art.
Respondent 1: You have to distinguish between art that is politically motivated and art that is merely propaganda (mind you, some propaganda is pretty crafty). Because if you take art that is politically motivated then you are wrong. Great art has been produced by people who wanted to make a political expression. Even Picasso stepped out his ivory tower to paint perhaps his most relevant work. Even Surrealism at its heart was political, a revolutionary movement.
That’s why I wrote “almost always” rather than “always.”
Respondent 2: It depends how cliched the politics is, and how cliched the art.
It is frequently the case that self-consciously political art (more properly described as politicised art) is didactic and/or clichéd.
Artists who want to pursue politics: step away from the easel and join a political movement.