Do you correct 'laymen'?

Working out at a clients and their staff are VERY opinionated.  I've stayed out of the discussions as to whether Niki Minanj is the new Madonna and whether anyone who can't trace their ancestry back to William the Conquerer should be allowed to be in the country, but when they started telling me accountancy 'facts' I struggled to maintain my polite demeanor. 

So do you correct laymen (ranging from 'man down pub' to non-clients/staff) or do you leave them in their ignorance (I swear there's a a bible quote along the lines of 'leave people alone in their ignorance, God'll get them in the end' but can never find it again)?

I'm not talking about staff and colleagues who need correcting, as that is their job and correcting them benefits the whole business.