Wait a minute.

If an audience of (just for example) of black or Asian people assembles, and an act of terrorism occurs, then who's going to be hurt?

Black or Asian people. Audience members, innocent bystanders, and men-in-the-street. Isn't that what we see in the papers every day? People gather (market, religious ceremony, procession) and somebody bombs the crowd.

So if the police think there is a danger of terrorism at concerts, they are trying to protect the audience. Is it so terrible of them to want to know what's going on, when, where and by whom?

As for less serious problems, if they are like the police here, they send a black officer to a disturbance among black people, and a white officer to a disturbance among white people. Experience just shows that to work.

I agree that the penalty sounds draconian, but the basic idea behind this is to protect the audiences.