From Despair To Where? The fatal error was to open the gate, especially when there were other options. Without that 1 action, 96 people would not have died. It was a negligent decision taken without reasonable consideration..
Disagree - the fatal error was not to block off the access to the tunnel leading to pens 3 and 4 when the gate was opened. According to the excellent Guardian article the closing of the tunnel was a known tactic to the police that even had its own specific name. It had been implemented many times before.
There was no "rush at the last minute " to get in to the game. There were problems beginning to build outside the Leppings Lane end before 2.30 and the police were not in any position to cope with this. Even once Gate C was opened at around 2.50 there was no rush or running to get in to the stand. There was a flow of 2000 people towards the natural entrance ahead of them - the tunnel to pens 3 & 4. If the tunnel had been closed off this wouldn't have happened.
Basically due to the hubris and arrogance of the Chief Constable, an inexperienced Match Commander was put in charge of the match who was incompetent and incapable of carrying out the duties required to keep the fans safe. IMO that is solely where the blame lies.