On Sunday, as the moron who ran on to the pitch after Robin van Persie's winner in the Manchester derby was led away, other fans applauded. You just hope they were applauding the efforts of stewards rather than the invader.
In fairness, when a Leeds United fan ran on to the pitch and pushed the Sheffield Wednesday goalkeeper Chris Kirkland in the face in a Championship game last month, most other supporters seemed appalled and the fan in question was quickly identified.
Manchester City fans, similarly, have a responsibility to hand over not merely whoever it was who threw the coin that hit Rio Ferdinand, but anybody who hurled missiles at the pitch - and there were plenty of coins and other objects thrown as Wayne Rooney tried to take a second-half corner.
Already the two ludicrous extremes have been out making their preposterous cases. United players did not provoke City fans: they celebrated a winning goal in a derby. That is allowed, and to suggest otherwise is preposterous.
But equally football is not back in the dark ages.
Yes, there does seem to have been an increase in fan misbehaviour, from sporadic pitch invasions to racist chants, but it remains small-scale.
Sadly, a crowd of 50,000 will always include a few idiots who get overexcited or see a sporting rivalry as some sort of life-and-death struggle. The issue is to ensure they remain a tiny minority and that they are punished.
Supporters groups, quite rightly, object to the notion of "fans" as a blanket definition, something that has been used for years to corral them and limit what would seem basic rights.
With all Premier League grounds covered by CCTV cameras and each fan, in theory at least, in a designated seat, isolating the perpetrators should not be too difficult.
But the notion of personal responsibility cuts both ways. Fans must help in policing their own. And they really must desist with complaints that football is becoming "too sanitised".
By all means mock the opposition, and if a player really has betrayed your club then take him to task for it. But know there is a line.
Racist or homophobic chanting clearly is taboo and so are other taunts that are harder to categorise.
Breaking the fourth wall and entering the pitch is an outrage.
When the fences came down after Hillsborough, there was an unspoken understanding: fans knew why the fences had gone up and they knew the tragedy they could cause.
Anybody tempted to run on a pitch or defend an invader might remember that.
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