The science of nature must be reductive for two reasons: 1.) nature is a cause and source of natural things; and 2.) we only need a science if the thing we are looking for is not evident. The science of nature therefore exists only because a source and cause of natural things is not evident, which gives rise to the need to reduce the natural thing back to its source.
Nature is a source. People get confused about this: nature is not some thing, like a forest or a volcano or a beating heart. Forests are natural, in the sense of coming forth from nature (there is an extended and romantic sense in which we call the forest “nature”, which is fine, but it not the sense of nature we seek to understand by “the science of nature”) Nature is the source or cause of the coming forth, which is a very different thing. We find nature by tracing things backward to some source from which they arose- a source which they are in some ways only a participation in or a manifestation of (not all reductions are the same).
It is pointless to complain that some account of nature is reductive. If it were not reductive it would not be a natural science- and yes, I do mean “reduction” in the sense that it is now used. The only question is whether the reduction is done rightly, or if one reduction is taken as the only possible one, or if we seek to reduce what is in fact nature, and thus not reducible.
“Reduction” and “reductionism” are words similar to “anger”. Since immoderate anger is so common and well-known, we tend to use the word anger to mean immoderate anger; and since bad reductions are so common, we tend to call “reductionism” an incorrect reduction. But this is an error on our part that we should strive to purge out: just as the Stoics got a very distorted view of moral philosophy by confusing anger with immoderate anger, we can get a very distorted view of natural philosophy by confusing reduction with incorrect reduction.