Actually, any church that feels the need to protect illegal immigrants (or other criminals, for that matter) should be allowed to do so, but only under the terms of traditional grants of sanctuary: the persons granted sanctuary cannot leave the church grounds, and must subsist entirely on charity from the faithful and clergy of the church. If they leave the church grounds, they are subject to arrest.
Let's see how many churches actually care enough about the "dignity" of migrants to provide them sanctuary if they have to do it the way it was always done.