You may define down, or otherwise minimize, as rigorously and deflectively as you like the term 'tainting.'

smooth and I prefer the functional definition, elucidated via praxis.

IE, if you wish to move your coins, but are prevented from doing so by consequence of some third parties' ostensible interest in them rather than technical obstacles, they are by the common understanding 'tainted.'

The nightmare scenario for you Old Whales is a whitelist, where by default movement of all non-permitted coins is forbidden.

Did you read the linked reddit discussion?  Peter Todd makes some good points in this area, albeit on the shaky grounds of the slippery slope trope.