Unfortunately, if you are a member of a group with a bad rep, you tend to get tarred with the same brush even if you are perfectly innocent. Unfair, but that's how it is.
LFC fans had a track record of going on the rob, not least in Europe. Not all, of course, but enough to get them a reputation. There's no denying this, as I've seen them boast of it, not least on RAWK. (Just as some on here boast about their 'hooligan' activities back in the day.)
Pre-Hillsborough, football fans in general - that is all of us - had a bad rep. But within that, LFC fans had one of the worst reps out there, which was, in a sense, quite an achievement.
This is one reason why so many people were ready and willing to believe the worst after Hillsborough. Yes, it was prejudice, and it was unjust, but you can see how it came about. I suspect if the Rags or Millwall (to name two of the obvious) had been involved instead, they would have been treated exactly the same.