...we should acknowledge that there are some good-faith arguments against "it would be good policy if every single person here without authorization were to be deported without exception."

Agreed. In fact, I make some of them. I take exception to the "without exception". As stated, I would oppose that policy. There are a long list of exceptions that could be written. I think a supporter of that type of policy is not operating in "good conscience".

The case you created is very gray. Do we put a statute of limitations on illegal crossings? If not, the being here 20 years takes on a different tenor. On the one hand, the person has made a life without incident here. OTOH, they aren't authorized to be here. Very gray. If they married a US citizen, even grayer. Do we deport the spouse of a US citizen who has otherwise not committed any crimes? Maybe impose a fine, and give a path for citizenship (which marrying a US citizen can legally do already)? It's tricky.