I am not sure whether you are inquiring about lawyers who are immigrants or lawyers who represent immigrants. I can explain what some people might consider bad about either group. However, while I understand what is not so good about a lawyer who is an immigrant, as an attorney who understands the ethical obligation of attorneys to represent people, I see nothing at all bad about immigration attorneys myself.
A person who has trained to be an attorney, who is from another country, is not going to be properly acquainted with the legal system of the country he or she is emigrating to. For example, a British attorney who emigrates to the United States, even speaking the same language and now in a legal system that is based upon the British legal system, cannot function effectively. The state and federal systems of law, the regulations, and even the procedures are going to be alien to that person. This is why nearly all jurisdictions in the United States require that one attend an accredited American law school and why all jurisdictions require an attorney to pass a state bar exam to practice law. So, this is the basis upon which there is something "bad" about an attorney who is an immigrant.
Now, as for immigration attorneys, those who represent immigrants, I am guessing there are people out there who feel that immigration lawyers are helping immigrants find loopholes that will allow the immigrants to remain in the United States, somehow contributing to what they perceive as an immigration problem. So, I suppose they are "bad" in the sense that attorneys who represent murderers are bad, since they are perceived as helping bad people get away with things.
However, every attorney is ethically bound to represent his or her client zealously, which means doing everything legally possible to secure that person's rights. This is a tenet of American law and society. The attorney is obligated to see to it that a person gets, at the very least, due process of law. If this results in an immigrant being able to stay in the United States, isn't that better than letting the government throw people out without giving them all of their rights? Attorneys are here to be sure the government is acting legally, fairly, and responsibly. If that is a bad thing, then I am for it!