Why is mixing good whiskey with cola/ginger ale frowned upon?
It is about the same thing as putting A-1 on prime rib. Mixers, like cola or ginger ale, tend to mask the flavors of the whiskey, something which is understandable for an 'inferior' brand but is thought of as 'taboo' for a 'fine' blend. The drink that results from mixing your fine whiskey with the mixers is (roughly) 'the same' as if you had mixed a cheaper blend, having concealed the subtleties that aging and craftsmanship have worked to create. 

That said...if you like it, it is your drink.