It's ethics as well as economics.
But economics is the key part - the simple matter is that the touts only exist because people are willing to pay the extortionate prices. If everyone had a similar mindset to me, the touts would not exist as nobody would ever buy from them. I'd rather not go to the gig than pay £90 for a £45 ticket.
I even know of someone who bought tickets for a gig (not Muse) and the tickets then sold out. One of his friends made him an offer above face value and he accepted the offer as he wasn't that fussed. I can see you have a grasp of economics so you'll know that it's just market forces in action again, just from the other side.
Ticket agencies / bands can do all they like to stop this but the touts will always find a way. The photo ID idea is probably the only way to wipe it out, but it'll be so costly that everyone will end up paying even more inflated prices anyway, and defeat the point of it.
Of course I'm purely focussing on the traditional touts outside of the gig venues.
Then there's eBay. Part of me says they should point blank refuse to allow people to sell tickets for anything more than face value (+ service charge) and a reasonable delivery fee (i.e. no more than £5). Allowing people to list them with starting prices of over twice the face value is horrendous.
But at the same time, how is a ticket for a gig any different to any other commodity? People sell CDs for more than they cost originally. People sell first editions of novels for more than they cost originally. Does the fact the tickets have a price physically printed on them actually make any difference? It still ultimately boils down to whether people (are stupid enough to) pay for the tickets at silly prices.