Because of intolerance.
Personally I wouldn't want people supporting an extremist islamic group to get the jail either. You don't change peoples views, no matter how repulsive they are, by making them illegal. It pushes them further underground, and further entrenches people. The green brigade's views are going to be repulsive to some, I fully understand that, but we can't let a political class dictate what is right or wrong. or in the case of the bill, where you can be more wrong, that's verging on the totalitarian groups like al Quieda and ISIS.
You're wrong on the count that the bill is getting people arrested for things that are already illegal, but certainly convictions for it have all been for things that were already illegal. You're right on the burden of proof though, it makes it very easy to get arrested now, as the police only need to say that your actions may have offended any right minded person, or that they could have caused disorder, even if measures were in place to prevent disorder. That isn't right.
The bill helps perpetuate the notion that we, as football fans, are all working class yobs, that drink, fight and offend, as we all know, that's far from the truth. It suits a political agenda that makes football fans look loutish, and it suits the police to collect extra money to make us look like apes.
It doesn't matter what else we as Motherwell fans stand for, we should be standing against this act of parliament.