I don't know about this 'prevailing wisdom' but I do know that you would like your hammock to be breathable (or at least as breathable as possible with the insulation you are using) when you are overheating and dealing with sweat, or sensible perspiration. On the other hand, I also know that you would like you hammock to not be breathable when you are dealing with trying to stay warm and are only dealing with insensible perspiration-- if you know how to deal with it.
It is not a situation where one case is always the best choice. Wise hammockers that use a breathable hammock with breathable under side insultaion (underquilts, pea pods, etc) often add a vapor barrier between the hammock and the underside insulation to extend the low temperature range. It is like whether to use a tarp that allows air flow or one that closes off and blocks the wind. A nice cool breeze is one thing, a blast of frigid air is something else. Just like a net hammock wouldn't be a wise choice when snow camping, a non-breathable hammock wouldn't be a wise choice when camping in 85F weather. Those are extremes and in the middle range where we typically are, there are shades of gray, so to speak. You will run it to situations where one might be preferred over the other and situations where there isn't that much difference. I wish I could snap my fingers and make my hammock switch back-and-forth between being very breathable to being non-breathable. While I am wishing, it would be nice if I could wave my hand and adjust how my tarp is pitched as well.