Science without a belief system is possible, but practically speaking, everyone carries some baggage. For instance, the "scientific method" is a belief system unto itself, the way most people apply it.
I think the notion of keeping an open mind is separate from the science- important for scientists, but not part and parcel. I think the real key to avoiding a "belief system" is to be willing to challenge anything- including whether you are willing to challenge anything, and to require evidence before regarding something as even qualifying as "information" much less "fact".
I think you're correct that scientist will have some baggage and beliefs, but I think science and the scientific method shouldn't have any belief Science seeks to know what is true, or failing that, be the least wrong thing we know. I think it's very important omit beliefs from science and test nature as we find it.
Science is absolutely based on beliefs. There's no way of getting around this. They may be mostly such fundamental beliefs that it makes little to no sense to seriously doubt them, but they're still beliefs. Or call them assumptions if that makes you feel better about it. As Shibboleth says, the admission of assumptions does not tarnish the reputation of science. Rather, it's the refusal to admit this that riles many people up.
When people refuse to admit the assumptive foundations of science, or suppose that a purely pragmatic view is sufficient, they are essentially denying the need for an explicit philosophy of science. This view couldn't be any more wrong. As Dr. Novella put it quite succinctly on Neurologica
: "There is no science without the philosophy of science, even if it is implied and not implicitly understood by scientists." When working scientists are completely unaware of the philosophical baggage associated with what they are doing or deny its existence outright, while simultaneously extolling the unquestionable awesomeness of the endeavor, it's not too hard to understand why some academics (especially those in the humanities) walk around mumbling phrases like "science worship".
None of this means that science is somehow a flawed method that needs philosophy to show it where it's going all wrong; all it means is that explicit reflection on one's own assumptions and methods is not only healthy, but essential for any endeavor which purports to uncover truth.