For those reasons I dont understand the point of the presentation to which you link 421C
2 of the pilots had FAA IRs, one an IMCr and one a PPL. I suspect they all thought that they were applying "a certain level of intelligence, presence and ability to assess situations". To me it illustrates, amongst other things, the seductive danger of making up your own rules because you judge it to be ok.
On the subject of relevance, how is the Milk Float story relevant to Nick's question? What analogy are you drawing between that and a pilot confronted with a solid overcast, as described in his question?