Given that the special forces of the UK were tied up with the G-8 protests and given that the militants knew it, I suggest that the protests contributed to the London bombing.
That is to say, the protests in Scotland diverted the necessary units from devoting attn to acts of terrorism. Therefore, the G-8 protestors are responsible for the bombings, if indirectly with the increasingly foolish protests.
The protests become increasingly foolish even if they are a carnival, a party, a place for one to stamp a passport and claim belonging, because the effect was achieved at Seattle, so that the tactics have to become more mature. If you want to end poverty in a global way, then put forth proposals to the G-8. Breaking the law, and bashing in Starbucks isn't terribly helpful these days. And it did divert the police attn so that 50 people were killed by terrorists in London.
Take responsibilty for the deaths of primarily working class Londoners, who live in comparative poverty, who fight the war in Iraq, while protestors have the luxury of cavorting and insulting the police. It doesn't mean the war in Iraq is right; it does mean that your tactics are frivolous, pointless and harmful.
Then, if you are truly democratic and independent, write of the attacks in London without a polemical bias, and write of what might not have happened if the special forces units were tied up babysitting middle class youth dressed up like carnival characters and protesting for the sake of protesting. Then, you will have an independent media.