Religious nut: "But you don't know *to a certainty* that the Sun will rise tomorrow, it could be blown up by aliens." = You can't know anything unless you know everything = You can't know anything unless you are God = The only place to get surety is the Church

So the "everything is a shade of grey" thing is an instance of rational people accidentally accepting a religious premise (that only God can know anything). We are accidently defining "knowledge" by a religious standard. We are letting them set the terms of the debate.

A secular concept of "knowledge" would start with the human being as the standard, not God, so therefore the light, light greys would be defined as white (since they are the best *we* can do). It's not fair to disparage ourselves because we don't live up to an impossible standard which it was irrational to define our concept of surety in terms of in the first place.