The fallacy in your thought process is that you can't imagine how the world changes if the scalpers disappear.
Today's reality: A guy discovers a band he likes is playing in town in 10 days, hops on to stubhub, and buys a ticket at 300% markup.
Your fantasy world where scalpers magically disappear: A guy discovers a band he likes is playing in town in 10 days, hops on to Ticketmaster and buys a ticket at msrp.
Actual reality if scalpers magically disappeared and prices stayed the same: A guy finds out a band he likes is playing in town in ten days and tries to buy a ticket, but he finds out that the entire concert sold out 5 months ago and he is just shit out of luck.
You may believe that a scalper holding a ticket hostage for a higher price adds no value, but the mere fact that you buy from them at all is a testament to the value they created: they held on to a ticket that you were too fucking slow to buy, and kept it out of reach to all the people who were poorer than you, and did so long enough for you to realize that the concert existed and you wanted to buy a ticket to it. And you begrudgingly admitted that that value was worth the markup you paid the minute you consented to buying it.