> If someone did want to do something at such a sporting event, nothing is stopping them from doing it at the gates where there is a reliable and unsecured mass of humanity

Theres a mass of people, but few cameras. Much worse cost/benefit ratio in terms of whatever craziness terrorists would supposedly consider benefit.

(feel free to spend the rest of your day thinking up silly wordplay involving "bang for the buck", I wish you were alone in this if you do)