Well, Berti, I obviously do not know whether any given Tory supporter has a wife and children/grandchildren. However, if they do, I suppose you would expect them to have forbidden the former from ever shopping at Sainsbury's or the latter from spending a penny on any item of Harry Potter merchandise...books, cinema visits, DVDs or whatever. Why? Well, Lord Sainsbury and J K Rowling have been major Labour donors for years. The list could go on.
As you yourself say, "It would be difficult to spend your time ascertaining exactly what every single product of this group are in order to boycott them."
The point there surely is that it's a matter of swings and roundabouts, isn't it? Labour supporters are buying products provided by Tory donors and Tory supporters are buying products provided by Labour donors...and they always will if the products are to their liking. Eeksy-peeksy!
That's why I think your notion is absurd. But what the hey!