Hindsight is a wonderful thing, but personally I'm never sure it's such a good idea to try to do these sorts of things during a game. Of course in a perfect world there's no reason not to, and there's never any excuse for that kind of behaviour. But unfortunately most supports probably do have an element that's capable of behaving like that, and you just can't predict what might happen on the pitch to rile them, or even just distract our own fans, before or during whatever was planned.