Individuals have every right to make their own decisions on how much time to allow to make a plane. If CO publishes rules regarding what time gates close, that is when they should close (except in the event that EVERYONE booked for a flight is already aboard). I can think of many times that I've cut it close, sometimes I've even been in the airport but taken a few extra minutes to go to the toilet, buy a newspaper, or finish up on my computer at the PC.