Opinions do cause behaviours, yes. But the key principle here is that we should censure any resulting behaviours, not the opinions that are supposedly behind them.
Otherwise we are slipping into a consensus that someone can be punished for what they think, whence it's a short step to punishing people for what someone else thinks they think. Whence it's but a step for people to be maliciously accused of thinking punishable things, and how can that kind of accusation be rebutted? The Soviet Union and the medieval Catholic Church had thought crime, and I think one of the major ways our culture improves on those is the absence of same. I would not welcome its return, however well-intentioned and motivated by a dislike of racism it is.
Start allowing thoughts to be deserving of punishment and you're on the road to somewhere deeply sinister.
(As an aside, I don't think the whole of UKIP is simply a manifestation of Farage's opinions. You are granting him rather more power than I think he has. The causes of Ukip are complex and part of a Europe-wide phenomenon, and certainly won't be effectively addressed by costuming yourself as a gay donkey and chasing his kids away from Sunday lunch.)