Not out of any disrespect for the victims of 2001 but because it is Catalan national day, marking the defeat of the City by Spanish forces in 1714. It unleashes the young and the rebellious on to the street proclaiming about Spanish imperialism, the police being an occupying force, Madrdid fascism etc etc.
We ate in the heat of the old town where there was quite an impressive demo going on with the Catalan flag draped everywhere, and revolutionary speeches made from a podium to cheering crowds. Whereas Britain's revolutionary gatherings now tend to be addressed by 80 year old Trots, the two speakers we saw both looked under the age of 16. I presume they were on early so they could get home and be tucked up in bed by their mums.
Still if it is all piss and wind (as we say up north) it is non-violent piss and wind. Apart from the odd firework left under a lamppost proclaiming the start of a Catalan people's bombing campaign, and attempts by various hooligan groups to blackmail Barca, nothing has exploded, nobody has been maimed or killed and nobody is left missing their loved ones on 9/11.