Why don't they just agree to come down like a ton of bricks on anyone who commits violent unprovoked assault on someone else whatever category they are deemed to be in? Am I missing something, but what actually does pigeon-holing everyone in this manner achieve in practical terms?
This.
The police have plenty of powers to deal with violent assault on a person, irrespective of the motives for it. It's not really clear what extra is added by making it a hate crime, apart perhaps from giving a signal to goths or whoever that the police will take seriously an assault on them. But they should do that anyway.