The problem with describing a view as 'extreme' and the person who holds it as an 'extremist' is that it assumes some nearby point relative to which the putative extreme and putative extremist are thus distantly situated; and it assumes that it's the very distance that matters. Take the idea that people are to be considered extremists if they 'fail to condemn the killing of British soldiers in Iraq or Afghanistan'. Not even if they approve of or condone it; if they merely fail to condemn it.
I've got news for those who drew up the guidelines. On the basis of that one, they're going to find a lot of extremists among the readers of the major liberal newspapers in this country: people who don't condemn the killing of British soldiers in Iraq or Afghanistan, but set themselves to 'understanding' it, and/or mumbling, and/or uttering, with darkened brow, the names of Tony Blair and George W. Bush. But in fact, judged by reference to what is standard, socially 'normal', dinner-party conventional, such people can't be extremists; they're right over here, in the middle of things, where 'our' sort of people are. In any case, what is wrong with their failure-to-condemn alignment would not follow from its being extreme. Extreme can sometimes be good - when the truth is, as it were, out on a limb and the reigning consensus morally cowardly or misguided. No, what's wrong with the alignment is that it's politically blind, complaisant towards forces fighting for the triumph of political tyranny and social reaction.