There is a massive confusion here.
There is nothing wrong with a partisan atmosphere at a football match. Football is sport, competition and people go to support their team, to encourage them. This may involve singing, cheering, waving flags and scarves and even booing on occasions to show disapproval of foul play by an opponent.
The trouble is that some on here want a hostile atmosphere and hostility has no place in football. LFCJax praises the "hostile" atmosphere in Turkey because it "can seem to stop you from playing, it sucks the life out of the away side and energizes the home side." This is not football but its exact opposite. It is, of course, intimidation and it is to prevent football, competition and what fans want to watch. Indeed the "hostility" has spilled over into murder in Turkey as Leeds United fans (and others) will testify. We have experienced the "hostility" of the Naples crowd. So have Bayern Munich fans, but a couple of them are too dead to remember.
This is the trouble with "hostile" atmospheres. They actually culminate in systematic booing of opposition players and it can last for the whole 90 minutes. Unfortunately, there are darker forces on the fringe of football that do not understand exactly where the limits of "hostility" are. Support for their team has given way to a hatred of the opposition, so that before the booing some are involved in throwing missiles at the other team's fans (on Sunday), or at the other team's players (usual for Liverpool against against United). I noticed that Brendan Rodgers had talked of "unleashing" the Liverpool crowd before the match. I can only assume that he was too preoccupied by memories of Hillsborough to remember what happened when Liverpool fans "unleashed" themselves on fans of Juventus in 1985.
Talk of "hostility" in football has no place and always spills over into behaviour which will destroy the game.