One possible explanation is that Sade and Femi's father always insists on the importance of the truth. He's a fearless journalist renowned for his critical articles on the hypocrisy and corruption of Nigeria's political leaders. It's a dangerous business as many in similar situations to Papa have paid for their lives by speaking out against the regime.
And it's that other side of the truth that Uncle Tunde emphasizes in trying to dissuade Papa from writing articles attacking the government. Papa believes he's doing the right thing, but Uncle Tunde regards him as selfish and stubborn, risking not just his own life but the lives of his children.
What the central conflict between Papa and Uncle Tunde illustrates is the inherent complexity of truth. The truth can be liberating, but also dangerous for those brave enough to seek it.