A topic of strong opinions, no doubt! I'm becoming convinced that I shouldn't have bought that powder-blue tang for my nano...
Seriously, though, all the "minimums" are subjective and -- as stated -- all are considerably less than a natural habitat. It probably is an oxymoron to consider yourself a responsible reefer, although we all want to do our best not to be cruel. A bird in a cage, a fish in a tank, a dog in a kennel. All represent WAY less than ideal situations, but pet owners do all of that, with love and care. How small can the tank, kennel, cage be? How big, before we smile to ourselves and assure our consciences that we're the 'good' owners?
There's a note of truth in Steve's comment. I am a bit interested in a fish that would outgrow my 37. It would take some time, and lord knows what tanks I'd have talked myself into by then. I'm not convinced one way or the other. I'm not a sentimentalist. If a fish isn't a good fit, I'll find it another home, and move on to the next one.