The question isn't about due weight between sources, though. It's about due weight with regards to information. To take a step back, clearly this was basically a brutal murder and, within the context of British society, you would have to be a lunatic not to condemn it unequivocally. It's always possible to dig up a lunatic if you want to interview one, but it doesn't change the basic consensus about whether the attack was a good or a bad thing. It's the consensus that the lead of the article ought to reflect. The views of people like Anjem Choudary, the Westboro Baptist Church or David Icke don't really have a place in the lead sections of articles about significant contemporary events.