What is the specific set of knowledge that delineates those who are "living in the ivory tower" from, to use a term introduced by another poster down-thread, "blue-collar programmers?" Do I become an ivory tower programmer as soon as I express any interest at all in functional programming? Or is there some level of FP knowledge ("first-class functions and recursion are acceptable, but no ADTs!") where you start "living in an ivory tower?" Or perhaps if I use these things in an industrial context it's okay, or does simply knowing about monads or Prolog mean I'm relegated to the ivory-tower ghetto?

Does understanding how a database works on a level past what most industrial programmers need to, say, leverage the value of an index make someone an ivory-tower resident? How about understanding how Paxos (ha) or Raft work? For that matter, does reading any computer science paper take me out of the realm of being a "blue-collar" programmer or does it depend on how much the paper stinks of "ivory-tower-ness?"

Have I made my point yet?