Why they didn't go through the processes to become legal? I don't know. But if they are just trying to live a new life in America, then we should let them stay, just make them become a legal citizen
To tell the difference between the good and bad, see if they are or have done anything illegal like I said before. Surely a quick glance at their criminal record could show whether or not they are "good" or "bad"
Not every immigrant who came here illegally commit crimes and do illegal stuff. I'm just saying we should deport them if they are doing illegal stuff (say drug related stuff, murder, etc etc). If they came here illegally, but they aren't actively doing anything illegal, then let them stay, just make them do the stuff to become a legal citizen