And...so? Are we drawing the line that only certain criminals are to be detained now?

It's not drawing lines. We're engaging in an effort to talk about the issue that recognizes the value frame of the other side.

I go back to the metaphor of "Javert Is Not The Hero". In Les Mis, the actual hero of the story - Jean Valjean - is a criminal. He stole a loaf of bread in order to save a relative from starving. The idea here is that not all people that have committed a crime deserve the same treatment, and that some people who have committed a crime can still be - or are - good people. The lesson that Javert learned, and committed suicide over, is that justice requires proportionality.

Bear in mind that Every. Single. Illegal. Immigrant. is a criminal by definition.

That is not true. Many, if not most, people who are here illegally have not committed crimes. Either because they entered the country legally and had their status changed after they got here (asylum applicants, overstays, people here under TPS status that was later revoked), or they were brought in as minors.

Why would we diminish all these other offenses? These folks are here illegally, were arrested for additional crimes, and convicted.

No, they weren't convicted. Again, 72% of the detainers were issued to people without convictions. These are people that have been arrested, not being released from prison.

We don't "diminish" these other offenses by treating them differently than, say, murder or rape. You'll get a different sentence for a minor assault charge than murder, because the crimes are different - we recognize that there's different levels of culpability for a bar fight than an actual killing. Justice requires treating many offenses differently from each other because they are of different magnitude. A criminal justice system that treated deliberate murder and simple assault identically would be an unjust system, and that same concern can underly a deportation system as well.

I think you're missing the point of the conversation, here. The premise is that people place a different priority on the deportation of people who are genuinely violent criminals (the murderers) and the people who have done something wrong but are otherwise generally decent folks. The folks that Newt Gingrich wants to have a "national conversation" about (see below link). You might place very little value on trying not to completely disrupt the lives of the people who are otherwise generally decent folks - the exercise we're engaging in is to try to acknowledge that not everyone shares that perspective on how much to weigh that, and try to articulate your arguments within the balancing framework that they have.

thehill.com - Gingrich immigration reform conversation