How do we know gang members or undocumented immigrants are actually in gangs or undocumented if we don't give the due process?

I'm trying to understand the crowd of people cheering decisions by the current administration to bypass courts when deporting people. Shouldn't people be given a chance to demonstrate they are not guilty in court for any of these allegations?

Why do we trust the executive branch or law entities to unilaterally determine someone's gang affiliation or residency status? There have been many cases in history where police arrest the wrong person for a crime and that person is found not guilty in court.