Another consideration that hasn't been talked about yet is that undocumented survivors who have already been identified by service agencies and law enforcement could also be arrested and/or deported under a law like Arizona's. Survivors of human trafficking go through various stages of immigration relief and the amount of time between them also varies. A survivor could go months without status while a law enforcement agency applies for continued presence (a temporary status, typically one year, that allows a survivor to stay in the US during an on-going investigation), federal certification or while a legal service provider applies for a T Visa (a more long-term immigration status set up through the TVPA).
During this time, service providers work to assist survivors to gain English skills, temporary housing, in addition to providing for other personal needs, but they are free to explore and walk around their community. While service providers can safety plan with survivors, the idea of explaining a law like that to an undocumented survivor who is waiting for immigration relief seems extremely challenging and, I would safely guess, add to the fear of law enforcement that survivors often already have.
Simply because a survivor is working with a law enforcement or service agency does not prevent another law enforcement agency from arresting and deporting them under this law because other law enforcement agencies would not have access necessarily to that individual's case. And, again, even though a person has been identified as a pre-certified victim of trafficking, they may still be considered undocumented and be without any form of government ID until the paperwork has gone through on any status application. If survivors are arrested or worse, deported, that negative experience could be extremely traumatic to that survivor (or worse) and damage any investigation or prosecution; all of which would be serious injustice for survivors.