Comment by Bran_son

"Illegal" refers to a person's presence in the country, not any specific action. If you would prefer to call them "trespassers", be my guest. But "undocumented" is deceptive - it implies they're allowed to stay, and they're just lacking documentation, like losing a passport. When in fact even fully documenting their presence and identity (such as during deportation procedures) doesn't mean they have permission to stay in the country.