> But if far right parties are gaining votes

Which votes are those again? In the USA, which we're talking about here.

If refusing to patronize 1 nazi means the far right gets more voters, we would expect to see that in USA election results over the last year or so.

Fortunately, this hypothesis is not borne out in the data. In fact, I'd say your purported correlation is inverted, but I suspect there is a deeper, correlated variable: "doesn't like nazis" -> ( "doesn't vote for nazis", "doesn't patronize nazis" ).