Subwoofer: should we even use them at all?

Elegal,

Those do exist. Duke at Audiokinesis makes a really interesting speaker system with your choice of two different subwoofer arrays, one sealed the other ported. There are four subs with four channels of amplification in either array. I think it's worth visiting his web site to check out.

There are also traditional 2.1 systems out there, tho not as many as there once were.

I've been using subs since '98 with excellent results. I think the trick is the right low pass xover and slope. I run my mains, Revel M106 full range and use a Velodyne SMS 1 to apply the low pass slope and freq which is steep and at 60 Hz. I use a REL R305 sub, it's 10" driver is perfect for music and plenty for movies.

It's nearly impossible to locate where the sub is, it blends perfectly. I also run the SMS 1 's EQ to tame a nasty 40Hz room mode. I have a very compact 2.1 system that sounds way better than it has a right to.......it would not be the same without the sub

Should we? Should you, should I?

Answers: No. Maybe, absolutely.

Is there any other audio subject that is so subjective and fraught with as many room, system, and media, variables as extra low frequency reproduction?

If there's ELF on the recording and you want to hear and feel it and you're using passive speakers then you might want to at least audition a properly integrated sub/s in your room. Keep in mind even the term, "properly integrated," is subjective.