Complex sentence: Cicero was asserting that the killing of Clodius was admissible so long as it was an act of self-defence; postulating that in extreme cases, where one's own life is immediately threatened, violence without proper regard to the laws is justifiable.
Split into simpler sentences: Cicero was asserting that the killing of Clodius was admissible if it was an act of self-defence. In extreme cases, with one's own life is immediately threatened, regardless of the laws is justifiable.