I guess what you mean is something along the lines of if we are used to "X is natural" used as an argument to "X is true", then we assume it is meant so every time we hear it,even when it is not the case? But I think for that to happen, first the fallacy must be commited often enough to become used to it? If nobody ever used "X is natural" in the sense of "X is good", why would we jump to this implication?

My point is, the implicature is rather social, usually, perhaps if you figure out a really unusual implicature, you will not really assume people making it. You will assume so when you have heard it so often that you got used to it. An example is that capitalism-is-bad carries the implicature of socialism-is-good. The only reason it carries it is simply the frequency of it, for it is most often socialists who criticize capitalism.

In other words, the whole thing may not be much more than a frequency based prediction: people probably mean what they most often mean.