Well some bloody idiot opened the gates (and indeed, the CC was sued - see for instance CC v Hicks).
NONE of that behaviour is acceptable Trouteater - and no right thinking person would think it is - whether it is verbal abuse (of whatever nature), throwing objects, excrement or making attacks. I am appalled that all Liverpool sought to do was apologise - they should have asked the police to investigate and if possible reported the perpetrators as well as banning them for life.
However, are you saying that there should be a law allowing footballers to go an attack the person they perceive to be guilty of abuse/throwing stuff etc?
Funnily enough I saw a case today where immediately after the full time whistle a footballer perceived that an opposing team member had said something abusive. His reaction? To run over, punch this guy to the ground knocking him unconscious. As it was he had got the wrong man. But that's OK presumably, cos footballers have to put up with crap?
Football has tried bloody hard to clean up its act in the years since I used to go (the two are NOT related!), unfortunately, there are a hard core of idiots, who call themselves "fans" who in fact are there to cause trouble. They should be routed out and banned. It shouldn't be down to players or other fans to retaliate with violence else where will that take the game?