Arne Saknussemm was persecuted for his ideas. What ideas might have been considered dangerous for Arne Saknussemm to believe?

Arne Saknussemm, a fictional character from Jules Verne's "A Journey to the Center of the Earth," held ideas that challenged conventional beliefs about the Earth's structure and the possibility of subterranean exploration. His advocacy for the existence of vast underground landscapes and the potential for adventure in the depths of the Earth could have been seen as heretical or blasphemous in a time when religious and scientific views were often intertwined. Additionally, his defiance of established science and exploration norms could have led to accusations of promoting dangerous or forbidden knowledge.