No matter if it's based on "science" it's still a "belief system". It might seem logical and "based on scientific evidence" (whatever that means), but a "belief" in "non belief" remains a "belief". There's a great quote about "believing is seeing" not "seeing is believing". Theories remain an issue of belief, not truth.
Incocknito has already given a pretty thorough answer; I wish only to make a couple of observations from a different angle.
First of all, science is not a belief system. It is primarily a mode of inquiry, and only in a derivative sense does the term "science" apply to the results of such inquiry. These results may be objects of belief or disbelief. But they are not science itself; they are merely the results--at a given moment in history--of the practice of science.
Second, it is of no relevance to the practice of science whether you or I or anyone else "believes"--that is, accepts--some scientific finding. What makes it a finding is the fact that it has satisfied a process of evaluation and testing, not the fact that some scientists believe it. In fact, the relation is exactly the opposite: the scientists believe it, or rather accept it, because it has been established by scientific procedures.
The doctrines of a religion, by contrast, can
only be explained as beliefs: the personal relation of the individual to the doctrine is not an incidental matter, as in science, but is absolutely essential.
Of course, people who are without scientific expertise may say, and often do say, that they believe or disbelieve this or that scientific finding (e.g., evangelical Christians who reject evolutionary biology). But they are not doing science: they are merely opining about science. Their beliefs about science are no more a part of science than the calculations that I make are a part of mathematics.
