If there is an equal way for all to purchase tickets then of course you should be able to re-sell tickets.  But in an unregulated industry such as live events.  2 Problems exist.  a)  There is an inequality in initial ticket distribution where the average person doesn't stand a chance against the "bots" to purchase tickets fairly and b) there is no way to prove a ticket is valid and therefore the system gets abused by anybody being able to produce a fake ticket that the average person can't tell the difference.  Add that to it being re-sold on a web-site that looks real with a money-back guarantee and you have over $1B in fraud a year in the industry.  That's why!