I still think its all seater stadia thats to blame to an extent.
at roker, cant remember who it was against, maybe the mags, one of their players went in for a tackle and I shouted OFF OFF OFF (it was fairly inocuos) and in 2 minutes i think 15,000 fans were shouting it.
I went to a U2 consert at leeds (most if not all standing), they had a crap rap support band on, they played 1 song, I shouted out, "Get the **** off the stage, you are crap", 10 seconds later 50 ppl shouted get the **** off, 1 minute later 4,000, they asked should we play another one, about 30,000 shouted get the **** off, and they went "suppose thats a no then" and went off the stage lol
on the other side of the coin, my dad went to see clapton at the albert hall a few years back, clapton was just strumming on the guitar for about 10 minutes, my dad shouts "are you going to play that bloody thing or what" and most of the audience just looked at him and either tutted or went SHHHHH.
Suppose what i am trying to say is, standing is a lot more spontaneus in your actions than sitting is, 1-10 ppl start singing or shouting when you are standing, a lot more join in, than when they are sitting, you wouldnt shout in a library where you are sitting down, you woudnt shout out in a cinema, you wouldnt do it at Christmas dinner (well depends how pissed you were lol).
PS: we could make up a new goal celebration like Man City knicked Lech Poznans, what it could be though thats unique to us i have no idea, but if its just fun and not offensive it may get those that dont usually get off their seats, joining in.