Let's assume for one moment that it's okay to carry on in day VMC, good vis., i.e. CAVOK.
Assume also that it is not okay to continue at night, in cloud etc.
If it is marginal (by which I mean, anywhere in between), where does the line lie? Let's face it - we've already by the assumptions above said there is a line.
If he has ground contact 50% of the time, does he need to go around? How about if he's "VMC on top" of a thin layer? How deep does the layer have to be?
In the mean time, the alarms start sounding. There's a pause while he evaluates the conditions, deciding whether or not to continue. That pause could be fatal in just the wrong situation.
Far better, in my book, to play it safe every time. Train in an instantaneous response. Don't program into a pilot's mind a delay in reacting to what could be a life-or-death, urgent situation. If it proves to be a spurious warning, then agree amongst yourselves that that's what you've got, and what you're going to do with it.
Two aphorisms that we've all said at one time or another. Firstly, nobody ever collided with the sky. And secondly, trust your instruments. If playing safe and taking a possibly unnecessary go-around is not butch enough for some people, then so be it. If going by the book insults your intelligence, then save it for working out why you got the problem in the first place.