> If the scalpers didn't exist, the eventual ticket-holders would still be able to purchase from the original vendor.

A lot of them wouldn't, though. If the scalpers sell the tickets for, say, $500, then the people willing to pay $500 get tickets pretty reliably. If the scalpers didn't exist, those people would have to take a roll of the dice along with the many, many more people who are willing to pay $45. A lot of them wouldn't be able to see the show.