> This is exactly the source of the trouble. Hearing scientists project their value system onto everybody else destroys their credibility.

> sticking to the facts and avoiding ideology and values

I think a few different things are being confused here, but as far as value is concerned, the choice to do science, to take scientific findings into account and to decide what to investigate are themselves the result of value judgements. There is no fact-value dichotomy. There is no "clean" separation between fact and value (as if value were a dirty word contrary to fact).

This fact-value dichotomy can be tied to the materialist worldview which denies objective value because it presumes a metaphysics that renders the world a kind of theater of senseless extension in space. Any value must therefore be a matter of subjective projection (and therefore delusion, putting to one side materialism's inherent inability to account for subjectivity). But this metaphysics is, to put it gently, problematic. The wish to separate fact from value (which I take to occupy one order, not two) is no doubt further encouraged by liberalism's pretensions to neutrality and the inherent tension within Lockean liberalism between science and liberty.

But I do agree that the actual deciding of policy is not to be left to scientists but to politicians and the like. Scientists are specialists who can supplement our knowledge in specific ways that generalists can then take into account along with other data and understanding when making judgements.