> You can do science without holding any beliefs just like birds can fly without a theory of aviation.

In which case your metaphysical assumptions will simply be implicit rather than explicit. For example, in doing science, you'll be "explaining" things, which assumes a certain position of the nature of explanation and causality. You'll be choosing a theory out of a number of competing ones, a choice which will rely on some assumptions (e.g. simpler is better?). You'll be trying to uncover "laws of nature", which would assume their existence in the first place, etc.