I'm coming at this from a similar (but not identical) point of view to the one gness posted earlier.
If all the fans had ...
1. Arrived in good time
2. Had correct, valid tickets
3. Gone to their allocated area
4. Been stone cold sober
... then it is possible (or even probable) that the disaster would not have occurred.
But ... in the fetid, violence-ridden swamp that was football crowds in the 1980s the chances of all the above happening was so vanishingly small as to be insignificant.
So - they needed :
5. A sound marshalling/policing plan with an adequate number of experienced police personnel controlled by experienced officers.
This was manifestly not the case - and a prompt, truthful report/enquiry could easily have established that (whilst also exposing any possible culpability from individual fans or groups of fans).
Why didn't this happen?
I simply refer back to a comment by Mrs O on page 1 of this thread - which she made about "Liverpool as a city", but I have amended it slightly :
"The British Police stick together when mourning their own, which is commendable, but they also stick together when denying responsibility for their wrongs, which I find abhorrent."
The lies, deceit and criminality of the Police in the aftermath of Hillsborough made any attempts to find the true causes of the disaster virtually impossible, and (ironically) have now resulted in all the blame and opprobrium being heaped on the Police themselves - when it is more than likely that they were actually far from being the only guilty ones on that day.