Well, for a mechanically inclined person with the money and time to get obsolete and discontinued parts and do all service and repair... OK, that makes it a hobby. You're right as usual.
Using a classic/antique motorcycle as daily transport is not sane. I'll except older (post-knucklehead) Harleys from this, parts and mechanics to keep them running are still pretty easy to find.
Riding a bike as your only transport except in the circumstances you list is not completely balanced either!
Here in Toronto the riding season for sane people is 5 months or so, slightly nutty or immune to cold and it's 7 months, more is just crazy. Simply using a motorcycle for daily transport proves you insane: I have seen a few bikes out in the last few days when the snow has gone from main roads and I don't envy the riders. It says a lot (and nothing good) about our transit system when anyone would take out a motorcycle here in December.