I don't think enough people have enough empathy to comprehend what it means to deport somebody. You're severing them from their familial ties, their economic opportunities, their entire life. Imagine you've been somewhere for 10 years, and suddenly they put you on a plane and dump you off in what is notionally your "home" but which probably no longer is.
I think I worked illegally somewhere once. I never quite figured it out. Bureaucracy is messy. I'm a person from a relatively privileged background and existence, but if suddenly they had said "uh, sorry, we can't pay you anymore and byebye" it wouldn't have been a small thing. And if I had a spouse? Kids?
Most people in the US can't imagine themselves in that situation. For various reasons, I can. Deporting people who have been here awhile is a horrible, mean, punitive, pointless thing to do.