Is "Illegal Immigrant" a Slur?

Charles Garcia, columnist and CEO of Garcia Trujillo, argues that the term "illegal immigrant" is a slur (from CNN, "Why 'illegal immigrant' is a slur"):

When you label someone an "illegal alien" or "illegal immigrant" or just plain "illegal," you are effectively saying the individual, as opposed to the actions the person has taken, is unlawful. The terms imply the very existence of an unauthorized migrant in America is criminal. … New York Times editorial writer Lawrence Downes says "illegal" is often "a code word for racial and ethnic hatred."

This is a claim that has frequently been made before. Naturally, The Civil Debate Page isn't in favor of slurs or name-calling, but is the term "illegal immigrant" a slur? Does it amount to saying that everything about the person or people it refers to is illegal?

I don't think it does. And I say that because, when we call someone a "legal alien", we aren't saying that everything about that person is legal. All we're saying is that the person, in immigrating to this country, followed the law. We're not commenting on whether "the individual, as opposed to their actions" are legal, or whether they're law-abiding with respect to any other laws. For instance, there's nothing contradictory in saying, for instance, "a legal immigrant broke the law by committing burglary". Calling someone a "legal immigrant" isn't a compliment, so I don't see why "illegal immigrant" must be a slur.

Likewise, if I say someone is a good driver or a bad cook, I'm not commenting on whether or not they are good or bad people, just whether or not they are good or bad at driving or cooking. If I were to call someone who practices medicine without a license an "illegal doctor" or someone who runs a business without the necessary permits an "illegal contractor" or "illegal vendor", would that be considered a slur against them as people?

Or, suppose a US citizen entered the US from another country without presenting a valid passport at a recognized port of entry (something that US citizens are legally required to do when returning to the US): If I call that person an "illegal entrant", is it a slur? Does calling someone an "undocumented immigrant" imply that everything about them is undocumented?

Garcia mentions that the term is used as a code word for racial and ethnic hatred. I wouldn't be surprised if it sometimes is, but I'm also sure that it sometimes isn't. And this is a problem with the allegation of "code words" or "dog whistle politics" in general: What is the standard to determine when a certain phrase is being used as code versus when it's not being used as code? It's very easy to accuse someone of using a phrase as a derisive code and, when they deny it, replying, "Well, of course you deny it, otherwise it wouldn't be code!"

So, it's not clear to me why the term "illegal immigrant" should be taken as a slur, coded or otherwise.