The argument is that it must be difficult for attorneys to endure the moral dilemmas brought about by defending clients whom the attorneys know to be guilty. On its face, your contention seems plenty reasonable. However, an attorney can represent a downright guilty person—and represent the client honestly and ethically, without any moral dilemmas: because the adversarial process involves more analysis than a true-false analysis of commission.
For example, attorneys can and do represent cases without the attorney putting any mind toward maintaining innocence of the client. A famous case to which plenty people wrongly ascribe such representation was Plessy v. Ferguson (1896), where attorneys defended Homer Plessy against a charge of being black in the white section of public transportation (paraphrased). Popular misconception is that the defense argued not that Plessy was innocent—but that the law requiring racial separation was unjust. (In fact defense argued that Plessy was innocent—that he “was seven-eighths Caucasian and one eighth African blood; that the mixture of colored blood was not discernible in him, and that he was [thus] entitled to every right, privilege and immunity secured to citizens of the United States of the white race.”) Perceptions of Plessy drip with revisionism, but the analysis remains: knowledge of a defendant’s guilt will not necessarily cause pause for the representing attorney.
Another example of this fact is Roe v. Wade (1973), where attorney Sarah Weddington—herself, a child-murderer—conceded that her client was seeking to murder a child (that fact was not even a concern in the matter). Instead, the case turned on the Supreme Court’s invention (written by Republican Harry Blackmun) that to prevent a woman from murdering her child is a violation of the woman’s human rights.
Plessy and Roe, among many other cases, remind that plenty lawyers are far from concerned about “right and wrong”—and instead aim only at persuasion: legalistic might-makes-right. Moreover, those pieces of jurisprudence remind that plenty cases (as well as the respective and collective minds of many lawyers) turn not on the guilt or innocence of any defendant—but rather on a strict (indeed, an often myopic, self-important, and counterproductive) reverence towards judicial process.
1. 163 U.S. 537.
2. Id. at 541.
3. 410 U.S. 113.
4. See Rachel Cooke, Sarah Weddington, Roe v Wade attorney, on Trump’s threat to abortion rights (The Guardian 2017) (“The US lawyer in [Roe] . . . talks about . . . her own decision to [murder a child] while she was a student”), available at theguardian.com/world/2017/mar/12/sarah-weddington-roe-v-wade-lawyer-legalise-abortion-america-donald-trump.
5. Note 3.
6. See id.; see also Planned Parenthood v. Casey, 505 U.S. 833, 874 (1992) (citing Hodgson v. Minnesota, 497 U. S. 417, 458-459 (1990) (O’Conner, J., concurring in part and concurring in judgment in part); Ohio v. Akron, 497 U. S. 502, 519-520 (1990) (opinion of Kennedy, J.); Webster v. Reproductive Health Services, 492 U.S. 490 (1989) at 530 (O’Conner, J., concurring in part and concurring in judgment); Thornburgh v. American College of Obstetricians and Gynecologists, 476 U. S., at 828 (O’Conner, J., dissenting); Simopoulos v. Virginia, 462 U. S. 506, 520 (1983) (O’Conner, J., concurring in part and concurring in judgment); Planned Parenthood v. Ashcroft, 462 U. S. 476, 505 (1983) (O’Conner, J., concurring in judgment in part and dissenting in part); Akron v. Akron, 462 U. S. 416, 464 (1983) (O’Conner, J., joined by White and Rehnquist, JJ., dissenting); Bellotti v. Baird, 428 U. S. 132, 147 (1976)) (inventing the judicial-supremacist myth that the U.S. Constitution requires that preventing a woman from murdering a child must not place an “undue burden” on the would-be murderer (“Only where state regulation imposes an undue burden on a woman’s ability to [murder a child] does the power of the State reach into the heart of the liberty protected by the Due Process Clause”).