Why should someone be stopped from using a pub just because other people who happen to support the same football club might cause trouble? If you use that logic in other situations there would be uproar. Imagine saying all black people must be jailed just because one went shoplifting. You can't assume everyone is a hooligan. Most Millwall supporters want a few drinks, a game of pool and an enjoyable day out at a club they are unlikely to ever visit again. Police are supposed to help people, not go out of their way to cause problems.
You have a valid point in that it is unfair to tar everyone with the same brush. I feel genuinely sorry for the decent Millwall fans who have had their club's reputation battered by a minority of troublemakers. The genuine Millwall fans deserve as warm a welcome as any visiting supporter on Saturday.
The thing is, you have to do things sometimes to the detriment of a majority if it means preventing a possible problem among a minority. I don't like waiting longer at airport security with liquids in plastic bags, having to take my shoes and belt off, being frisked. But its being done with the right intentions. I went to a match in Belgium and had to show ID and have my name checked off a list because the fact that I'm English might make me out to be a hooligan! I didn't like that either but I can understand why its been done.
If people want a drink on Saturday, they can get one. If, as it has been suggested, a lot of Millwall fans are going into Manchester first then I'm sure there'll be pubs there to take them. Our bar will be open on Saturday I imagine, so our fans won't go without. Quite why the police are getting the grief over this is beyond me.