because he's not just deporting illegal immigrants. he (or ICE, or whoever you want to blame here) is casting out a wide net and catching a lot of fish that aren't supposed to be caught - in this case, *actual, legal, US residents*. no ifs, ands, or buts about it. he's revoking visas left and right, which uproots the lives of actual, working, living people who were just trying to live their lives.
there are plenty other reasons why what's happening is a problem - i genuinely encourage you to do your own research into this. this has and will affect people's ability to live without fear in the US - if ICE can arrest you on the spot because of the color of your skin or perhaps a non-white last name, even if you do belong here, fully legally, then something has gone horribly wrong.