I will generalize your question a bit, hopefully this is still interesting to you too:
If the outcome of a debate cannot possibly have an impact on my (our) lives, then why take part in the debate? Why take any position?
I propose three possible answers. The first two may be seen as side-stepping the question, but still seem relevant to me:
- Philosophy can be practiced as l'art pour l'art, intellectual puzzling for its own sake; the problems are intriguing, we derive pleasure from reading a good argumentation, even if it's useless
- Debates are always embedded in a wider context. The direct outcome, the outcome sofar, or the expected outcomes, may not have an impact on the beliefs of the participants or the public, but there may be meta-values in play: The participants could be debating because that's how they make money as academics. The debate could exemplify to the listeners (for instance to children) how to conduct a smart, respectful, non-violent, debate.
- The boundary between questions that can be decided by empirical research and those that can not is fuzzier than it may appear. The boundary between the useful and useless may be fuzzier than it appears.
The l'art pour l'art practice of philosophy may appear as "useless" or even "frivolous". The endless debates of philosophers may appear to be abstruse and ridiculous to scientists. I believe it's an empirical fact that many scientists do not read philosophy and are not aware of what's happening in academic philosophic - and this doesn't seem to hinder them in any way in their pursuits.
The philosophical project of trying to "ground" science in an ultimate, unassailable, absolute truth - a truth that can be used as basis or scaffold of all knowledge, and that, once established will remain standing forever, the Truth with capital T that Descartes and Spinoza thought to have found - is no longer taken seriously by scientists, I think, at least not as a scientific project. The essence of science is not knowledge (a possible, but always contestable and unsure outcome) but research, inquiry. To conduct research and reach (temporary, mutable, conditional) consensus, we do need some explicit standards and methods, but those need not be ultimate or absolute. The standards and methods may change as we go along (which doesn't mean they are arbitrary or subjective).
Those relativist ideas about science - the ones I just hinted at - are themselves born from philosophical debates, scientific inquiries, historical studies. They hint at a philosphy of science that can itself not be totally scientific and is still somewhat up in the air -- up for debate. Also, there is a fuzzy border around science that leaves room for questions that currently are not scientific, or cannot be decided by science, but may at some point become so - because our theories and methods become more powerful, our language more expressive, or because we observe relations among phenomena that we didn't observe before.
Example: "Are atoms real? Do they really exist or are they just a mental construct, part of a theoretic model to explain certain processes? Parts of the atomic model may be testable but is the core assumption (that atoms themselves exist) verifiable?" Up to the last century, up to Einstein's study of brownian motion, this question could be seen as "metaphysical" or "borderline-metaphysical", with Ernst Mach as one of the last serious holdouts to advocate against the reality of atoms. But Mach lost this debate. As one chemist famously remarked:
We know that atoms and molecules exist because we can see them.
(P.W.Atkins, Physical Chemistry, 1986)
(Some crackpot philosophers might try to reopen this debate, but do we want to listen to them? Physicists will just shrug them off.)
ASIDE
A variation on that last debate actually lives on in the debates about observables/unobservables in so-called constructive empiricism. Personally, I side with Ian Hacking's criticism of the anti-realist, constructive empiricist position -- which is the position that there is a relevant epistemic distinction to be made between seeing things with the naked eye and (for instance) seeing things through a microscope. Van Fraassen's reply to that seems sharp, but also subtly misleading. Also, in its broad outline, I believe that constructive empiricism is misguided. -- In mathematics we can see that intuitionist, constructive mathematics is actually relevant as a mathematical project; it's being pursued by mathematicians, not just as a philosophy of math. Is constructive empiricism relevant in a similar way? Is it actually directly being carried by scientists and making a difference?