Keep that tin hat on for a while! Firstly, from all the personal and eye-witness accounts that have been retold here it is clear that there was no hooligan element amongst a group of fans that were legitimately making their way to the ground in a reasonable manner - in fact on transport that SYP had exclusive control over. These were the fans who were then penalised, according to them, because of a hooligan element at Sheffield Wednesday. If there really were trouble causes blocking the way, then why weren't they carted off in vans? If there weren't, then why assume that the two sets of fans can't be within sight of each other without WWIII breaking out? And 20 minutes after kick off, just how many Wednesdayites were not in the ground? In other words, it's total bullshit.
Secondly, when there is trouble, like the trouble you mentioned, the police don't seem to deal with it. At that moment they have the trouble makers causing trouble, but somehow nothing is done - it's far easier for them to send in battallions of troops to heard non-trouble makers in the name of prevention. It's a cop out.
Every incident is different, but on this occasion there doesn't seem to have been any problem that the police had to deal with.
I'll say it again, would you defend the police for treating all, let's say, muslims as potential terrorists on the basis that there has been trouble with muslim terrorists? We all want the hooligans and knobsticks to be taken out of football, but the establishment doesn't seem to be doing that, it has become acceptable for them to just "prevent" trouble by targeting any and every fan.