No, no, no--it can be completely a scientific distinction and doesn't need to have any metaphysical presuppositions attached at all (except the basic ones you need to avoid nihilism).

The brain is an organ whose purpose is detection of phenomena, prediction of future phenomena, and control of the rest of the body.

The liver doesn't do that.

If we want to understand how our body clears alcohol, produces clotting factors, regulates glucose, etc., then the brain is comparatively unimportant and the liver is comparatively important. In fact, in medicine it often is important to talk just-about-the-liver-as-opposed-to-everything-else.

But mostly, the complex (time-varying, high-information-input) problems which need solving are solved by one particular organ: the brain. Behaviors that are characteristic for one sex are...behaviors. It's a brain thing.

Declaring that we can't focus on what is interesting and different about one organ is completely anti-biological. Of course we can! And we do. It's just that--especially given that we occupy the "very smart animal" niche--we have a lot of brain-specific or brain-heavy concerns. Lots of emergent properties, too.

So it makes a good deal of sense to abstract away the brain function stuff into "mind". Yes, it's not a perfectly clean abstraction--if you're hungry, drunk, tired, etc., your body's biochemistry is going to impact the function of your neurons enough so your "mind" will be impacted. But it's a pretty useful way to focus on one extraordinarily rich aspect of the functioning of one organ system. And because of the hyperspecialization of that organ system, there are a lot of differences between that one and the rest.

Historically, we felt the distinction first (presumably based on the need for a representation in the brain of the rest of the body in order for the brain to properly plan and control the rest of the body; but a lesser need for a representation of itself because the control is mostly not explicit). We started talking about it before we knew how it works, and the language (and attitudes) reflect that history. But it doesn't mean we're forced to fail to make distinctions once we go with a 100% biology viewpoint. Indeed, making distinctions is one of the central tasks for gaining knowledge about biology (and everything else).

We can reject the metaphysical distinction between mind and body in the same sense that we reject Aristotelian mechanics--actually, in a lot of cases, Aristotelian mechanics have a good deal of sense to them, but we came to a more fundamental understanding and derive (much more accurately) the Aristotelian-style mechanics, where they are approximately true, from more fundamental mechanics (Newtonian, etc.). Objects in motion do tend to come to rest (because of friction, not because it is the nature of objects to do so), and it's fine when not doing anything too mechanically detailed to just keep "they tend to come to rest" that as a rule of thumb.

Doesn't mean we're endorsing Aristotelian mechanics as the truth. Likewise with mind/body distinctions.