What bearing does philosophy have in an entirely scientific debate?

It has to do with how we interpret the evidence that we find. Experimentation is useless without interpretation and philosophy guides interpretation. This is also known as the "experimenter effect" a bias that an experimenter isn't cognizant of but exists nonetheless. This concept is very central to fully understanding why we believe what we do as a group and outlines the tremendous difficulty faced in changing a deeply ingrained belief regardless of evidence.

Check out "What's Wrong with Relativity" from the menu to the left; an unbiased look at the sociology of scientific knowledge and its bearing on relativity.