You're putting on a late-night event at a South London venue featuring rap, garage and other 'urban' music that will be attended by huge numbers of black people. Do you:
(a) Assume there will be no trouble, and not bother much about security, or
(b) Mount scanners and staff with wands at the entrances and search the audience for knives and guns?
The O2 is also hosting Leonard Cohen. His audience are highly unlikely to be carrying any weapons beyond a rolled-up copy of the Guardian's supplement on Nicaraguan healthcare, so don't need to be searched. It's called risk assessment. Not racism.