Open borders, and no deportation ever, is a perfectly viable alternative.
how do you propose that the "delicate" infrastructure of the US can handle a clean doubling of population over the course of 1 year?
Not at all viable when you consider the cost of requisite social services to support such an initiative, which is one of the myriad reasons why no country has ever considered the option.
Germany's refugee crisis is a good example of the pros and cons.
How is it unfair?
The unfairness is that the bar for participation is being significantly lowered to the point where it risks the social safety nets for everyone. It's unfair to both native citizens and naturalized ones.
Make no mistake, I'm also against completely open borders without deportation, for a variety of reasons. "Fuck you, got mine" is not one of those reasons.