Final answer:
Gustave Courbet's 'The Stonebreakers' caused unease among the upper-class due to its realistic portrayal of poverty and labor, challenging conventional artistic norms and societal attitudes towards the lower class.
Step-by-step explanation:
Gustave Courbet's Stonebreakers alarmed upper-class viewers because a) It depicted scenes of rural poverty and challenged traditional artistic norms. Courbet, as a proponent of Realism, painted unidealized images of peasants and workers, a stark contrast to the traditional and romanticized subjects of the time. His commitment to depicting the real conditions of the lower classes, as opposed to the aristocratic or mythical, resonated with socialist ideals and brought light to social issues and realities of the day. Moreover, his technique—with rough brushwork and spontaneous handling of paint—stood in opposition to the polished styles of Neoclassicism, marking a progressive shift in the world of art.