Online Ticket Scalping, Ticket Resale Sites should be ILLEGAL

Have you ever tried to get tickets (Twenty One Pilots) and then it’s a SOLD OUT show? Well, it’s probably only sold out on Ticketmaster, but then you can go on Stub Hub, Vivid Seats, Seat Geek, Ticket Liquidator, Cheap Tickets, etc and find tickets. Concerts get sold out really quick because these ticket resale sites buy up all the tickets and then resell them for 5 times the amount. How is this legal? Why is this okay? This just seems to hurt the fans, the venue, and the artists. Please COMMENT below about what you think.