The analogy was that the person saying something being violent, racist scum doesn't necessarily mean that what he's saying is false or racist or nasty, but does tend to put other people off saying it because they don't want to sound like him.
If you look at The Political Compass page for this election [http://politicalcompass.org/ukparties2010], you can see that they've separated the parties along two axes not just one. They use left and right for the economic left and right, from state ownership of everything to private ownership of everything, with "you might not be totally screwed" in the middle, and up and down for totalitarianism and anarchy, from concentration camps and compulsory uniformed service to Mad Max world, with "you can live" in the middle.
On their chart, the parties are spread out as a set of dots:
Personally, I don't think a dot is really accurate because a party might be hard at the top on some matters and right down at the bottom on others, with a blur of stances on different issues between them.
Anyway, people vote for parties for various reasons, including "Me da alluz vorted Layb'r olliz larf, an' Arl doo t'same." Some might vote entirely on the economic stance. Some might vote on law and order or immigration or the environment. Everyone has different priorities. Even with just two axes, you'd have to mark each person's position as a dot with their flexibility making a series of elliptical contours around them, and they'd vote for the party inside the smallest ellipse that actually has a party in it as being the one with which they most agree.
The BNP are right at the top with Pol Pot and Adolf Hitler, above Josef Stalin, Sarah Palin and Alan Keyes. Coming down from there, you've got Robert Mugabe, Mitt Romney and Labour, then UKIP and Duncan Hunter, then Margaret Thatcher, Mitt Romney and the Conservatives, then Sarkozy, Aznar, John-McCain-at-the-start-of-the-Primaries and the Respect party, then eventually you get to the Liberal Democrats, then Dennis Kucinich, then Ralph Nader, then the Green party and then the Dalai Lama.
From right to left, you've got Ron Paul, Tom Tancredo, Newt Gingrich, George W Bush, Friedman, the Conservatives and UKIP, Thatcher, Berlusconi, Sarkozy and Aznar and the rest of the US Republicans, then Labour in amongst the Ehud Olmert, Angela Merkel and most of the US Democrats, then the Liberal Democrats, Kevin Rudd and more Europeans,
then the BNP, then it's Scottish National, Sinn Fein, Dennis Kucinich, Plaid Cymru, SDLP, Green, Ralph Nader, Gandhi, Respect, Scottish Socialist Party, Stalin, Pol Pot.
If someone's vote is based on a vertical bar on that chart, representing a really tight economic position and no interest in the "control - law and order - freedom - anarchy" axis, they could vote BNP because the Lib-Dems are just slightly too far to the right for them. If they vote based on a horizontal bar of degree of freedom with no interest in the economy, they'd see no difference between SDLP and Lib-Dem but be nowhere near the BNP, or not be sure whether to go Conservative or Respect. If someone has a position on the US political trend from centre to top-right, producing a voting preference map sloping top-left to bottom-right, they could see the BNP and Labour or DUP and Conservative as being about equally desirable.
Most people will have voted on a position based on a few factors rather than the whole manifesto.
