People here really don't see the difference between challenging someone who is out canvassing and interrupting someone having Sunday lunch with family members? 
And Hully I completely agree that racism is bad. But I don't believe it is right or beneficial to anyone - including those who suffer as a result of racism - to harass individuals simply for holding those opinions. Someone who bullies, attacks or otherwise harms people for being a particular ethnicity? Sure, punish them according to the law. Someone who we just suspect of racist thoughts? They are welcome to those thoughts.
Can't you see that once we see some opinions as inherently punishable, we open up the possibility of incredibly oppressive measures. Think of any historical context where people could be held to account for opinions rather than actions, and you've got a pretty disturbing list. Things like Soviet show trials, the Spanish Inquisition, McCarthyism to name but a few.
I know there is no comparison between Farage being pestered in a pub and the Spanish Inquisition, before anyone remarks on that. Of course there isn't. But the principle still stands. We can't start eroding individuals' rights to hold whatever opinions they want free of censure, or we're on a slippery slope to somewhere quite worrying.