Ever since childhood, the narrator has had a theory that the idea of God’s intestines is sacrilegious. God and “shit” are not compatible, he says, leaving him in an “either/or” situation. Either man has intestines because he was created in God’s image and God has intestines, or God really doesn’t have intestines and man is nothing like Him. As God has given freedom to humankind, He is not responsible for any atrocities that humankind may commit. God is, however, completely responsible for shit.
A couple of chapters later, Kundera also uses the word “shit” to explain his idea of kitsch and the role it plays in communism and politics. He says that kitsch is ignoring any “shit” that might be incompatible with life or a certain ideology, and ignoring God’s intestines is an example of such disregard. In this way, while God isn't responsible for humankind’s atrocities, He is responsible for kitsch, which often leads to such atrocities.