The simple answer is never.
Hard-core pornography is famously difficult to define, although one knows it when one sees it.
A spike point, on the other hand, is mindboggingly easy to define. A spike that wins a point. Convention allows that spikes the force errors from the opponent (control or ball handling) are also counted as spike points.
There is an argument that a net touch from the block should be considered as a forced error from the opponent. This argument is incorrect. A net touch is a purely voluntary action. No one forces a blocker to touch the net. It is a fault, an unforced error. It cannot, logically, be attributed to a spiker.
So in a note to all leagues and scoutmen and coaches who consider a net touch to be a spike point, please stop. You are wrong.