That’s a bizarre argument. Conduct is illegal because it’s bad or has harmful effects. Immigration laws exist because society recognizes that immigration has various undesirable effects (cultural change, strain on public resources, etc.), so we need to restrict immigration to controllable levels that manage those negative effects.

The objection to illegal immigrants is that they’re here. While deportation efforts should follow the law like everything else, there’s nothing about illegal immigration that makes the legal process especially important compared to other things.