On the issue of "What else can I do?", I think the general consensus in these types of circumstances is that we need to get a group of 5 or 6 kiters to approach the kiter together and "kindly suggest" they don't launch. If no sanity prevails, then simply deflating the leading edge should be the next cause of action, obviously with 5 or 6 kiters as your backstop. One on one, people tend to get aggressive, one on five or six, they tend to realise maybe they're making a mistake.
^^^^^^^^^^^^^^^^^
I recently saw someone who was trying to self launch a 12m Rebel with all the lines tangled in 30-35knts only 3 or 4 meters away from the wall at St Kilda, I had my kite in the air at the time but someone ran over and deflated his kite before he could launch it probably saving his life. He had never kited before and had no lessons.
When it doubt stop someone doing something stupid and ask questions later. He then put up his trainer kite and was again nearly blown off the beach before one of the instructors convinced him to go home for the day.
Imagine if no one had said anything, they would have to live with the fact that they might have been able to stop a fatality.
WHEN IN DOUBT SAY SOMETHING