It is always right to extend civility to others. That applies whatever you think of their opinions or behaviour.

There's a French family comedy series that was on a couple of months ago on a French channel. (Fais pas çi , fais pas ça - if you get a chance to see it that sometime I recommend it). At one point one of the families were entertaining someone, and in the curse of the visit she started coming out with the kind of racist views you often find among "nice" people, who assume you feel the same as they do.

There's a dilemma in such situations - do you flare up and denounce the views, or stay silent and effectively collude. But what the host does is neither. He politely says to the viisitor something on the lines of "You should be aware madam that you are on enemy territory", and indicates that she should leave without delay.