It displays the typical lesswrong mindset that lesswrong is the last resort of sanity

It's not a guardian of truth. It grew from insanity, so others may have as well - from Dennett to Drescher, there's no telling about the ideas of others until they open their mouths.

[extreme solution A.] Either that or [opposite equally extreme solution B.]

I choose a third alternative that's less extreme.

The very fact that we can discuss them means they affect our material world (e.g. by typing posts in this forum about them),

In the more general use of the word a causal relationship between the phenomena is implied: the epiphenomenon is a consequence of the primary phenomenon

The directionality isn't symmetrical, it only goes one way. Wikipedia:

An epiphenomenon can be an effect of primary phenomena, but cannot affect a primary phenomenon. In philosophy of mind, epiphenomenalism is the view that mental phenomena are epiphenomena in that they can be caused by physical phenomena, but cannot cause physical phenomena.