Double Standards.
If some guy had posted a group on Facebook organising a terrorist attack and it later turned out that the police knew about the group on Facebook but had done nothing about it - you would all be screaming that the police were useless and should of done something.
The group on Facebook at first glance seemed to be serious enough - certainly serious enough that I reported it. There were many many links to the group flying around on Twitter under the #riot hashtag. In the same vane there are many many people posting pictures to Facebook of themselves with all the stuff they have stolen - and even people trying to organise sales for stuff they have stolen.
It has got to the point where it is difficult to distinguish between those who are trying to be funny and those who are actually involved.
However - regardless of whether the group was serious or not - *some* people could have decided to organise something based on the initial idea of the group.
Additionally having just heard the poor shop owner "reeves" - in complete shock at his store being burned to the ground after 100 years of being there, and the dumbstruck woman who was watching the partyshop burn knowing that there were 3 flats above it - but completely helpless to do anything - it was in very poor taste for someone to suggest starting a riot elsewhere.