my problem with reductionism

I’ve never quite understood the reductionst program in the philosophy of science.
I’ve edited beaucoup papers and dissertations logically proving that, happily, the mental is a level wholly reducible to the molecular, or that the vital is reducible to the laws of physics without a remainder, and I’m the editor – I don’t interpose myself in the flow of argument and shout halt! These papers grudgingly reference the problems in the field, the fact that bridging principles seem to break down and that we still have no account that would explain the higher level phenomena completely, but in the end we can, on principle, correlate every mental and vital even to an underlying physical one, and that is all we need.
This is what they say. I begin to lose the thread with the word “underlying:.
Underlying. Higher and lower levels. In the arguments themselves these words are used with a, it seems to me, blissful unconsciousness. Because I still don’t know what level means, here.
It would seem that after we have done our tricks, we can abolish the level talk –and yet we can’t. The level itself, what it is, where it comes from, is the great stubborn residual here. Is it a fiction? I’ve not read a defense of the idea that the level is a fiction, and that underlying is simply a bow to rhetoric. Rather, it seems that we consider the level both a convenient conceptual device and a self-explanatory rhetorical conventionl. But it seems to me that the whole argument rests on there being a level that can be reduced.
If it is a rhetorical convention, it seems to me that it has sprung not from quasi-science or pre-science, but from the way the mind is. And if it is more than a convention – if it is sort of a natural fiction, like a mirage – then our story of reduction is certainly not finished if it can’t account for the mirage.

It is a puzzle, to me.