M. Tullius Cicero Pro P. Sulla 48

[48] Nor, indeed, can I make out why you are angry with me. If it is because I am defending a man whom you accusing, why should not I also be angry with you, who are accusing a man whom I am defending? “I,” say you, “am accusing my enemy.” And I am defending my friend. “But you ought not to defend any one who is being tried for conspiracy.” On the contrary, no one ought to be more prompt to defend a man of whom he has never suspected any ill, than he who has had many reasons for forming opinions about other men. “Why did you give evidence against others?” Because I was compelled. “Why were they convicted?” Because my evidence was believed. “It is behaving like a king to speak against whomsoever you please and to defend whomsoever you please.” Say, rather, that it is slavery not to be able to speak against any one you choose and to defend any one you choose. And if you begin to consider whether it was more necessary for me to do this or for you to do that, you will perceive that you could with more credit fix a limit to your enmities than I could to my humanity.