For a Christian, this parable explains more about what Jesus taught. According to Jesus we are to love our neighbor as we love oursleves. For Jews, this wasn't meant to love EVERYONE. So Jesus used the equivalent of a despised illegal alien (a samaritan) to demonstrate what kind of love he was talking about and what lengths we should go to.
Does our law on aliens allow for the kind of treatment Jesus says is our duty?
Sure they do. There's nothing illegal about rendering aid to the victim of a crime. Further, there's nothing illegal about paying for his hospital stay if you desire to do so.
So Jesus used the equivalent of a despised illegal alien..
Here's where you're on shaky ground. Where exactly in Luke does it say the Samaritan was where he was illegally? Chapter and Verse if you please.
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Jesus did not tell the Roman government what to do.