More to the point: what if you didn't know that the wonderful landscape was by Hitler?

It's the age-old dilemma - do you separate the artist as a person from the art he/she creates? If you know nothing of the one, then you can have no preconceptions of the other. The work of art stands alone, just as it is.

It's when you get to know more about the personal life of the artist that the difficulty arises.