Question: I am a lawyer. A potential client asked me to help sue someone who is known to be part of the underworld. Should I agree based on the commandment of lo taguru ("Do not be afraid of a man" - Devarim 1:17), or is it okay for me to pass?
Answer: The formal prohibition of lo taguru does not apply here for a few reasons. First it only applies to dayanim, as is evident not only from the context of the pasuk but also the context in which it comes up in classical sources (the Sefer Hachinuch #415 is explicit on this point; see Minchat Chinuch, ad loc.). There are some sources that extend lo taguru somewhat further (Sanhedrin 6b regarding assistants to dayanim; inference of the Meiri, Sanhedrin 89b regarding one who withholds prophecy out of fear). However, applying it to require a lawyer, who does not have a halachically formal part in the judicial process, to take a case is too much of a stretch. Secondly, even for a dayan, the prohibition applies only if he has heard the case to the extent that he has a feeling what the ruling should be (Sanhedrin 6b).
In general it is problematic to take sides in adjudication (Avot 1:8). While there is an opinion that this warning is only to a dayan (Shiltei Giborim, cited by Shach, CM 66:82), most poskim posit that no one should take sides without a reason (see Sha’ar Mishpat 17:5). What are grounds for taking sides? The gemara (Ketubot 86a) says that it is proper to advise a litigant if he is a relative, invoking a pasuk (Yeshaya 58:7), as long as the advisor is not an important person. The Maharshal (Shut 24) applies this approach to helping a widow who is a litigant. Logic dictates that this permission applies to fighting hardened criminals (see Yeshaya ibid:6), a task that a simple individual cannot handle alone.
In cases where giving advice is appropriate, is there an obligation or mitzva to help out as a lawyer? When the lawyer is (honestly) convinced that his client is correct, there should be a mitzva ofhashavat aveida to help him win his case (see part of the breadth of themitzva in Bava Kama 81b) and thus in the cases it is permitted to get involved, it should likewise be included in that mitzva.
However, the mitzva of hashavat aveida does not require one to put himself in a position of loss or hardship to save money for another (Bava Metzia 30a). This is all the more clear if there are any number of other people who can do the job, making the individual lawyer less specifically obligated than one who found a lost item (see one of many applications of this distinction in Bemareh Habazak I:32).
Returning to the case of the fearful dayan, the Shulchan Aruch (CM 12:1) rules that a dayan who has a set public role is required to hear the case when others would not. While the Radbaz (Sanhedrin 22:1) and Bach (CM 12) explain that it is because the public will help him, the Beit Yosef (ad loc.) seems to understand that one with responsibility cannot shirk it even in the face of reasonable concern. That logic would seem to apply to a lawyer with a role of district attorney, for example. We also find, in a parallel case, that the Tzitz Eliezer (IX:17) allows and encourages a doctor to expose himself to patients with infectious diseases as part of his job. That being said, the job description of an average lawyer does not necessarily include angering dangerous criminals, in which case he should not have to feel obligated to do so. When he decides he wants to, there is generally permission for someone to put himself into at least moderate danger as part of his pursuit of livelihood (Bava Metzia 112a).
In summary, a lawyer need not feel an obligation to take on a case in which he will have to go against a dangerous opposing litigant. He may choose to do so, preferably after discussing the matter with his family. This is a noble step if he has a unique opportunity to help someone who needs and deserves it.